Marine Weather of the Inland Waters of Western Washington

NOAA Technical Memorandum ERL PMEL-44

MARINE WEATHER OF THE INLAND WATERS OF WESTERN WASHINGTON

James E. Overland Bernard A. Walter, Jr.

Pacific Marine Environmental Laboratory Seattle, Washington January 1983

UNITED STATES NATIONAL OCEANIC AND Environmental Research DEPARTMENT OF COMMERCE ATMOSPHERIC ADMINISTRATION Laboratories Malcolm Baldrige, John V. Byrne, George H. Ludwig Secretary Administrator Director

CONTENTS Abstract 1 1. Introduction 2 2. Climatological Summary 2 2.1 Air temperature 2 2.2 Preci pitation 6 2.3 Cloud cover and fog 6 2.4 Wind and waves 12 2.5 Air qual ity 12 2.6 Surface hydrology 23 3. Large-scale Meteorological Characteristics 23 4. Regional Meteorological Phenomena 30 4.1 Overview 30 4.2 Gap winds and bora 32 4.3 Orographic low-pressure formation 36 in the lee of the Olympic Mountains 4.4 Effects of orography on precipitation--the 46 Puget Sound convergence zone 4.5 Diurnal wind variations--the sea breeze 51 and valley breeze 5. Summary 57 6. Acknowledgements 59 7. References 60

iii Figures Figure 1. Location map for western Washington 3 and southwest British Columbia. Figure 2. Topographic map of northwest Washington. 4 Figure 3. Annual temperature cycle at SEATAC 5 Airport (1945-1970). Figure 4. Mean annual precipitation (1930-1957) 8 for western Washington. Figure 5. Annual cycle of precipitation at SEATAC 9 Airport (1945-1970). Figure 6. Annual cycle of clear or partly cloudy 10 days at SEATAC Airport (1945-1980). Figure 7. January and July surface wind roses for 14 western Washington. Figure 8a. One-year time series of the N-S wind 17 component for West Point. Figure 8b. Frequency spectra for the north and east 18 components of wind for West Point during winter. Figure 8c. Frequency spectra for the north and east 19 components of wind for West Point during summer. Figure 9. Annual wave climatology computed for West 20 Point from the wind climatology at SEATAC Airport. Figure 10. Mean annual particulate concentration 22 for 1980. Figure 11. Mean annual runoff (m3 s-l) for Puget Sound. 24 Figure 12a. Mean annual cycle of discharge for 25 Puget Sound's three major tributaries. Figure 12b. Interannual variability of discharge 26 for Puget Sound's three major tributaries. Figure 13. Typical weather patterns (LIt L2 t HIt H2) 27 affecting the Pacific Northwest. Figure 14. Typical local wind patterns for the 31 passage of a front through western Washington. Figure 15a. Sea-level pressure analysis for 00 GMT 33 24 February 1980 for western Washington. Figure 15b. Local wind field on 23 February and sea- 33 level pressure analysis for 21 GMT 23 February 1980 for the Straits of Juan de Fuca and Georgia. Figure 16a. Sea-level pressure analysis for 00 GMT 34 14 February 1980.

iv Figure 16. (b) Local wind field on 13 February 1980 34 and sea-level pressure analysis for 21 GMT 13 February 1980. Figure 16. (c) Wind and dewpoint fields from surface 35 and aircraft reports 21-24 GMT 13 February 1980. (Overland and Walter, 1981). Figure 17. Surface map, 12 GMT 28 November 1979. 37 Figure 18. Cross section of potential temperature 38 (KO) across the state of Washington. Figure 19. Regional surface map for 12 GMT, 40 13 February 1979. Figure 20. (a) Sea-level pressure analysis at 41 00 GMT 19 February 1980, and (b) mesoscale wind and pressure field at 21 GMT 18 February 1980. Figure 20. (c) Sea-level pressure analysis at 42 00 GMT 29 February 1980 and (d) mesoscale wind and pressure field at 21 GMT 28 February 1980. Figure 20. (e) Sea-level pressure analysis at 43 00 GMT 10 March 1980 and (f) mesoscale wind and pressure at 21 GMT 9 March 1980. Figure 21a. Plumes from upwind stacks at various 44 elevations (after Hunt and Snyder, 1980). Figure 21b. Comparison of experimental and analytically 45 computed streak-lines in the horizontal plane at mid-level of a Gaussian-shaped obstacle for a Froude number of 0.154 (after Riley et al., 1976). Figure 22. Sum of the perturbation pressure field from 47 Smith's hydrostatic linear model and a hypothetical synoptic pressure field (Smith, 1981). Figure 23. Polar representation of the wind speed and 49 direction at Hoquiam, Washington, during ten convergence zone events (after Mass, 1981). Figure 24. Streamlines over the Puget Sound area during 50 the convergence zone event of May 2-3, 1978. Figure 25. Schematic view of the low-level flow during 52 a convergence event (Mass, 1981). Figure 26. (a) Summary of the number of times the lowest 53 cloud deck in Puget Sound occurred in each composite zone during five convergence zone events. (b) Temperature deviations (OF) from the Puget Sound mean for each composite zone. (c) Summary of the number of precipitation events that occurred in each composite zone during ten convergence zone events (after Mass, 1981). Figure 27. Annual variation of precipitation for the 54 rain shadow and northern, central, and southern Puget Sound regions (Mass, 1981). v Figure 28. Percentage contributions to total precipi- 55 tation at three coastal stations and three inland stations from warm sector, narrow cold-frontal, wide cold-frontal, and post-frontal rainbands on 8 December 1976. Figure 29. Resultant wind hodographs for stations 56 in the Strait of Juan de Fuca, north, central, and south Puget Sound for July 1950. Figure 30. Average sea-level pressures at each hour 58 of the day for July 1950 at Tatoosh Island, Port Angeles, Everett, Bellingham, and sea-level pressure differences between Port Angeles and Bellingham, Port Angeles and Everett, and Tatoosh Island and Port Angeles.

vi Tables Table 1. Probability of freezing temperatures for 7 three stations in the Puget Sound region. Table 2. Average total hours of sunshine and mean 11 daily total solar radiation for SEATAC Airport (1966-1975). Table 3. Percentage frequency of occurrence of fog 13 for all observations by month. Table 4. Monthly wind speed/direction frequencies 15 (1949-1958). Table 5. Annual average concentration of suspended 21 particulates for stations in the Puget Sound region (1972-1979). Table 6. Number of days per month with synoptic 29 weather patterns Ll, L2, HI, H2. Table 7. Comparison of winds reported by Reed (1980) 48 in Hood Canal 14-15 GMT 13 February 1979 and those calculated from Eq. 1.

vii

Marine Weather of the Inland Waters of Western Washington l

James E. Overland and Bernard A. Walter, Jr.

ABSTRACT. The mid~latitude, west coast marine climate of western Washington is typified in summer by high sea-level pressure as part of the North Pacific weather pattern and in winter by a sequence of storms which originate to the west. Mean and extreme temperatures are moderated by the proximity of the Pacific Ocean and Puget Sound, resulting in an mean temperature of 4°C in January and 17°C in August at Seattle. Local variations in precipitation and wind are influenced by both large-scale weather patterns and the region's topography. Fifty percent of the annual precipitation for most of the inland region falls in the four months from November through February, and less than five percent falls in July and August; the driest region is to the northeast of the Olympic Mountains. Over the inland waters, the winds flow from high to low sea-level pressure in the direction of the local channels. Recent studies by the University of Washington and PMEL on the Puget Sound convergence zone, sea and valley breeze, precipitation patterns and local wind patterns are summarized. The storm which resulted in destruction of the Hood Canal Bridge has shown that the presence of the Olympic Mountains can induce a regional low-pressure system in their lee which can result in strong surface winds over the inland waters.

lContribution number 595 from the NOAA/ERL Pacific Marine Environmental Laboratory, 3711 15th Avenue N.E., Seattle, Washington 98105.

1 1. Introduction The climate of the Puget Sound Basin in western Washington State is a mid-latitude, west coast marine type. The source regions of the predominant air masses reaching Puget Sound are over the Pacific Ocean; this produces a moderating influence on the weather in both summer and winter. A prevailing westerly-to-northwesterly flow of air associated with high sea-level pressure in the eastern Pacific results in a dry season beginning in June and reaching a peak in midsummer. l In the late fall and winter the high-pressure area retreats to the south allowing a series of storms to cross the region, thus effecting a wet season that begins in October, reaches a peak in winter, and decreases in the spring. This winter pattern is occasionally interrupted by the influence of continental high pressure which is accompanied by cold tem peratures and dry air. Topography has a large influence on the weather of Puget Sound (Figs. 1 and 2). The region is flanked on the west by the Olympic Mountains and on the east by the Cascade Range. The elevation of the region varies from sea level on the Sound to 2500 mand higher in the mountains. The Cascades and the Canadian Rocky Mountains shield Puget Sound from cold air masses moving south ward across Canada. To the west, the Willapa Hills (which lie south of Hoquiam, Washington), the Olympic Mountains, and the Coastal Range on Vancouver Island are effective in protecting the area from more intense winter storms that reach the coast by forcing orographic precipitation on the western slopes (Hobbs et al., 1975). The Strait of Juan de Fuca, the Strait of Georgia, and the Chehalis River Valley provide low-level passages for maritime air to move inland and are the primary determinant of surface winds. The next section provides a climatological overview of air temperature, precipitation, winds, and other important climatological variables for the Puget Sound Basin. Section 3 discusses the synoptic or large-scale distribu tion and propagation of high and low sea-level pressure patterns that influence the meteorology of western Washington. Section 4 provides a summary of a number of regional meteorological phenomena that contribute to the climatology of the region.

2. Climatological Summary 2.1. Air temperature The yearly cycle and variability of monthly mean temperatures measured at SEATAC Airport, 20 miles south of Seattle, are shown in Fig. 3. During the

lThe meteorological convention of specifying the direction from which the wind is blowing is used throughout this memorandum.

2 BRITISH COLUMBIA

VANCOUVER ISLAND 49

Mt. Baker

n» en n» 48 o fTl ~ o c Z »----1 Z en 47 N PACIFIC OCEAN ? 2,5 5.0 7,5 Iqo KILOMETERS

Figure 1. Location map for western Washington and southwest British Columbia.

3 ~ 0-300 meters o 30 60km M;!{:i.Vl 300-1500 meters

Figure 2. Topographic map of northwest Washington.

4 MONTHLY TEMPERATURE NORMALS AT SEATAC 25

20 -u o ---W 0:::::> 15 ~ 0:: W ~ 10 w r-

JFMAMJJASOND

--- AVERAGE MAXIMUM ---- MEAN ------AVERAGE MINIMUM

Figure 3. Annual temperature cycle at SEATAC (National Climatic Center, 1980). Values are the official normals (1945-1970).

5 summer months, afternoon temperatures at lower elevations are often 20°C to 25°C. Maximum temperatures reach 29°C to 32°C on a few days during a given year; temperatures of 38°C or higher occur infrequently. In winter, tempera tures in the Puget Sound lowlands usually range from 3°C to 7°C in the after noon and from -2°C to 5°C at night. Almost every winter the temperature drops to between -7°C and -12°C on a few nights, with the coldest weather occurring during a few short outbreaks of cold, dry air from the north or the east. The longest growing season, 190 to 220 days, occurs on the San Juan Islands and in areas nearest to Puget Sound. Variations of several weeks in the duration of the growing season can occur within short distances. Near the water, the average date of the last OoC temperature in the spring is mid-April, and the average date of the first OoC temperature in the fall is near the end of October (Table 1). Temperatures of -2.2°C or lower are usually recorded 15 to 30 days later (Phillips, 1968).

2.2. Precipitation The moist maritime air that reaches the Washington coast in late fall and winter is approximately the same temperature as the surface waters. Thus, orographic lifting and cooling of these air masses moving inland readily result in widespread cloudiness and precipitation. The mean annual precipi tation chart for western Washington illustrates the extreme horizontal var iation in precipitation (Fig. 4). The driest sections of the Sound are to the northeast of the Olympic Mountains and receive 45 to 75 cm of precipitation annually. Over most of the lowlands, annual precipitation ranges from 100 to 130 cm, increasing to 190 cm in the foothills and from 380 to 510 cm on the wettest slopes of the mountains. Due to the mild weather of the Puget Sound Basin, most of the precipitation below 500 m is in the form of rain. The yearly cycle of rainfall measured at SEATAC Airport indicates that a large variability of rainfall can be expected in any given month (Fig. 5). Fifty percent of the annual precipitation for most of the inland region falls in the four-month period from November through February. The combined rainfall for the months of July and August is less than five percent of the annual total. Since 1900 there has been a decrease and then an increase in the 10ng term trend of precipitation. The ten-year mean rainfall for 1901-1910 at Seattle was 87 cm; the mean then decreased to 70 cm for 1921-1930, and has increased to 93 cm for the period 1961-1970 (Church, 1974). Total snowfall in the Puget Sound lowlands is generally less than 25 cm per year and normally occurs from November to March, with maximum amounts in January.

2.3. Cloud cover and fog The P~get Sound climate is characterized by a high percentage of overcast days (Fig. 6). The number of clear or partly cloudy days each month ranges from 5 to 7 in the winter, 8 to 14 in the spring and fall, and 17 or more in the summer. Table 2 gives the average total hours of sunshine and mean daily total solar radiation (in calories cm- 2), by month for SEATAC.

6 Table 1.--Probability of freezing temperatures for three stations in the Puget Sound region* (at 0°, -2.2°, -4.4°C)

Spring Months Fall Months

Station Temp. 90% 50% 10% 10% 50% 90%

Bothell OoC Apr 18 May 13 June 7 Sept 12 Oct 5 Oct 28 (1931- -2.2 Mar 19 Apr 13 May 8 Oct 7 Oct 30 Nov 22 1952) -4.4 Feb 7 Mar 8 Apr 2 Oct 22 Nov 15

SEATAC OoC Mar 15 Apr 9 May 4 Oct 10 Nov 2 Nov 25 (1945- -2.2 Feb 5 Mar 9 Apr 4 Oct 26 Nov 17 Dec 16 1960) -4.4 Feb 9 Mar 9 Nov 20

University OoC Feb 26 Mar 23 Apr 17 Oct 26 Nov 18 Dec 11 of -2.2 Feb 2 Mar 2 Nov 21 Dec 18 Washington -4.4 Jan 17 Feb 19 Dec 3 (1931-1960)

*After Phillips, 1968.

7 MEAN ANNUAL PRECIPITATION, 1930-1957 WESTERN WASHINGTON STATE

I 1240

Figure 4. Mean annual precipitation (1930-1957) for western Washington. Contours are in inches (1 in =2.54 cm). (From Philipps, 1968.)

8 35 MONTHLY PRECIPITATION AT SEATAC

30 \ / \ / \ / / 25 \ ,/ \ ./ ,.-.. / E u "'" / '"-'" 20 \ / z " 0- \ / ~ \ / r- 15 J 0.. \ u- / w \ I 0:: \'/"" 0.. 10 \ / \ / \ / J 5 ,-' / , ,- " '-...... _-- ...... 0 --- J F MA M J J A S 0 N 0

---- GREATEST MONTHLY --- MEAN ------LEAST MONTHLY Figure 5. Annual cycle of precipitation at SEATAC (National Climatic Center, 1980). The mean is the official normal (1945-1970) and the extremes are for the period of record (1945-1980).

9 25 NUMBER OF CLEAR OR PARTLY CLOUDY DAYS AT SEATAC PER MONTH 20

J FMAM JJ A SON D

I I CLEAR DAYS OR PARTLY CLOUDY V/lJl//IM CLEAR

Figure 6. Annual cycle of clear or partly cloudy days (1945-1980) at SEATAC (National Climatic Center, 1980).

10 Table 2.--Average total hours of sunshine and mean daily total solar radiation for SEATAC Airport 1966-1975* (in Langleys, by month)

J F M A M JJ A S o N o

Hours of 61 122 180 208 274 257 318 287 230 140 75 45 sunshine

Total solar 80 162 266 390 513 531 581 478 353 203 98 62 radiation

*After Critchfield, 1978.

11 · Frequently during the summer and fall, fog or low clouds, 300 to 600 m thick, form over Puget Sound and the lowlands during the night and dissipate by afternoon (Table 3). In the fall, there is a high incidence of fog because of radiational cooling at night. In the summer, cool, moist coastal air is advected into the Strait of Juan de Fuca and northern Puget Sound resulting in fog formation.

2.4. Wind and waves Puget Sound wind patterns are influenced by mountain barriers and low level passages (Fig. 7). In southern Puget Sound the strongest winds come from the south to southwest when the more intense Pacific storms move inland. During winter, the occasional presence of high pressure over the interior of British Columbia can produce strong easterly winds blowing down pressure gradient through the Strait of Juan de Fuca (Reed, 1931). In summer, winds are generally light in the afternoons; a northerly sea breeze develops over Puget Sound and the lowlands, and a westerly sea breeze develops in the Strait of Juan de Fuca. Over the Main Basin of Puget Sound, extremes in wind speed can be expected to exceed 25 ms-l once in 2 years, 40 ms-l once in 50 years, and 45 m s-l once in 100 years (Phillips, 1968). The wind statistics for SEATAC are given in Table 4; wind statistics for other stations, including Bellingham, Everett, and Olympia, are given in the Climatological Handbook, Columbia River Basin States (1968). A study of regional wind patterns for western Washington and southern British Columbia is given by Schoenberg (1983). The time series of the N-S wind component and energy spectra derived from a one-year record (1975-1976) of winds at West Point, a representative location for the Puget Sound Main Basin, are shown in Fig. 8a (Cannon and Laird, 1978). The energy spectrum of both the N-S and E-W wind components for winter (Fig. 8b) shows peaks at 0.25 cycles day-1 (i.e., frequency of storm passage), and the spectrum for summer (Fig. 8c) has a diurnal peak in the E-W component indicating the dominant sea breeze/valley breeze influence between the Sound and the adjacent lowlands to the east. The height and dominant period of wind-waves are a function of windspeed, wind duration, and fetch. An annual wave climatology for West Point (fig. 9) was calculated from windspeed and duration from SEATAC and fetches for Puget Sound (Skjelbreia, 1981) using relations from the Shore Protection Manual (1973). The largest waves come from the south along the major axis of the Sound during storm events. In addition, a large frequency of intermediate height waves come from the southwest; in this case wave heights are fetch limited during the strong post-frontal southwesterly winds.

2.5. Air quality In general, air quality problems are less serious in the Puget Sound region than in other major metropolitan regions because of the proximity of the ocean and the tendency for considerable advection north and south through Puget Sound. However, pollutants accumulate during periods of stagnation when light winds or stable stratification prevail. Since 1965, the Puget Sound Air Pollution Control Agency has operated a network of monitoring stations through out the Puget Sound region to measure suspended particulates and concentrations of S02' CO, and 03.

12 Table 3.--Percentage frequency of occurrence of fog for all observations by month*

J F M AM JJ A S o N D Ann

Bellingham 8.4 5.9 3.2 1.3 1.7 2.1 2.4 4.5 10.0 17.4 10.7 5.1 6.0 Hoquiam 20.2 19.7 12.6 10.0 4.9 7.5 8.5 11. 9 14.9 19.5 28.6 26.8 15.2 Pt. Angeles 1.9 5.1 1.7 0.9 2.8 6.7 11.8 15.2 16.3 15.6 6.1 5.1 7.5 ...... w Everett 21. 8 20.7 12.1 7.7 7.0 12.5 11. 7 15.6 20.8 29.6 28.2 23.8 17.6 Olympia 23.5 23.2 14.7 8.4 4.1 4.8 6.0 9.9 17.9 28.8 30.4 25.8 16.4 Sea Boeing 13.7 11. 3 6.1 3.7 1.9 2.7 3.2 4.9 12.1 17.5 20.7 14.5 9.3

SEATAC 13.7 12.5 6.7 4.4 3.1 4.6 6.9 7.8 14.8 20.3 21. 2 14.5 10.9 Whidbey 5.6 8.7 4.0 2.6 2.5 4.5 8.4 10.3 14.1 20.7 15.9 6.6 8.7 Tatoosh 7.9 9.2 5.7 6.1 8.1 14.6 22.8 23.7 19.7 10.6 7.6 9.9 12.2

* From the Climatological Handbookt 1968. Most stations represent records for 1949-1958. #' . J~.II-EVERETT(2) ~l(E~)

'~Sl::ATTLE'(I) . ~33-NORTH "-----*41-NORTH t" BEND (I) " BEND(I) .,.. '43-TACOMA (2)

56- TACOMA (2) ~32- CHEHALIS (I) ...... *,22-CHEHALIS (I) 4=>0 . 37-CASTLE ROCK (I) '.!2~CASTLE ROCK (I) 24-KELSO (2) .24-KELSO (2) 4- NORTH HEAD (I)

46-NORTH DALLES (I) "":':. ',. ~ *- IO-NORTH DALLES (I) JANUARY JULY SPEED INDEX CLASS INDEX CLASS SCALE IN PERCENT OF TIME SYMBOL 2 III 16-314-15 121 13-314-12 II 1--. I 32-47 2 32-46 o 25 50 75 -- II 48+ 2 47+ ® ALL STATIONS HAVE THE SAME RANGE (0-3MPH)

Figure 7. January and July surface wind roses for western Washington (after Phillips, 1968). This figure must be interpreted with some care as strongest winds at each station do not necessarily occur during the same synoptic event. Table 4.--Monthly wind speed/direction frequencies* (1949-1958) for SEATAC

JAN U A R • FEB R U A R •

HCURLY CaSERYAT 10~S OF .I~O SPEEO HOURLY CBSERYATlO~S OF .I~O SPEEO "IUS PER HOUR "ILES PER HOUR

1 8 13 19 25 32 39 1 8 13 19 25 32 39 Ie TO• TO TO TC TO TO TO OYER AYE TO TO• TO TO TO TO TO TO OyeR AYE lolR 3 1 12 18 2. 31 38 'b .b TOUL SPEEO OIR 3 1 12 18 2' 31 38 'b .b TOUL SPEEO .. J .b ';.9 2.5 1.5 0.5 ).1 b.O 11.0 ~ 0.' 0.9 2.0 1.5 0.3 0.1 5.2 11.2 NNe J.3 1.) l.8 2.1 ".3 • b.5 11.2 ~He 0.' 1.1 2.9 1.1 0.2 b.3 10.b ~E J.l 1.1 2.2 J.l • 5 •• 8.2 HE 0.5 I.' 1.9 O.b • •• 5 B.5 E~E :i.l\ J .1 C.b J.l 1.1 1.0 E~E 0.3 0.1 0.1 001 I.B 1.0 E 1.1 2.J 2.2 O.B 0.1 bol 8.0 E 0.1 I •• 1.1 O.b •• 3 1.8 ESE 1. ) 3.·"" •• 9 1.2 0.1 1001 B.b nE O.b 2. B 2.9 1.0 0.1 1.5 8.5 ~E 1.3 3.1 '.b 1.0 • 10.1 1.9 SE O.b 2.1 303 0.5 • 1.2 1.9 HE 0 •• 1.B 2.b ).b 0.1 5.b B.l SSE 0.3 2.0 2.2 O.b 0.1 • 5.' B.l S ';.3 1.5 3.1 3.e 0.9 0.2 9.b 12.2 S 0 •• 1.1 3.5 2.9 0.1 0.2 9.3 11.b SS. J .2 J.B 3.1 5.' 2.2 0 •• '.1 12.B 1'.1 SS. 0 •• 1.1 3.1 b.l 2.B O.b 0.1 1••9 1'.8 S. 0.3 J.l 2.3 •• 1 2.b 0.1 • 10.B 15.6 S. 0.3 0.9 2.B '.b 3.3 0.1 12.1 15.5 .S. J.2 J.' J.l O.b 0.3 J.2 • 2.3 13.2 .S. 0.3 0.1 O.B 1.0 O.b 0.3 3.5 13.3 0.1 ~.3 ·J.2 • • 0.1 1.5 0.2 0.' 0.5 0.1 0.1 1.3 B.5 • •.~. j .2 J.I Jol a•• 5.8 0.2 0.5 0.2 . • · 0.9 b.O ~. · ~. .". J.I ".2 Jol 0.5 101 0.2 O.b 0.3 . • 1.2 b.l ~.3 · ~~. if",.. .,;,.It ::'.4 ·).3· J.1 1.5 9.b 0.1 0.1 1.0 0.' 0.1 2 •• 10.1 CUll 9.3 9.3 CALM 11.b 11.b TOTAL 1b .b 19•• 33.5 21.b 1.3 1.b 0.1 100.0 9.9 TOUL 11.' 19.b 30.b 22.0 8.' 1.9 0.1 100.0 10.0

)II IRe ~ APR I L

HOURL. CBSERYAT ICHS OF ••"0 sp~eo HOU~LY OBSERYATlO~S OF .I~O SPEEO ~ILES PEA HOUR MILES PER HCUR

1 8 13 19 25 32 39 1 B \3 19 25 32 39 T~ TO• TO TO TO Til TO TO OYER AYE TO TO• TO TO TO 10 10 TO OYER AYE UlK 3 1 12 18 2' 31 3B .b 'b TOTAL SPEEe OIR 3 1 12 18 2' 31 38 'b .b TOTAL SPEEO

N 0.2 J.B 2.2 1.1 ".2 5.1 11.1 ~ 0 •• 1.1 3.1 2.1 0.3 0.1 b.9 n.9 ~~E J •• 1.J 2.1 1.5 0.2 5.B 10.2 ~~E 0.2 1.2 3.3 2.0 0.3 1.0 11.0 ~E J .b 1.2 2.J ).7 '.5 8.5 ~E 0.5 1.B 2.B 1.2 0.1 b •• 9.1 ElfE 0.3 ~.B 0.9 J.2 · 2.2 1.9 E~E 0.3 O.B 1.0 0.2 2.3 1.9 E O.B 1.5 1•• J.8 .J·.1 '.b B.5 E 0.5 1.0 1.0 0.3 ·• 2.8 1.5 E ~E J •• 2.3 3.2 1.0 0.1 1.5 B.5 ESE 0.3 I.B 1.1 0.3 0.1 3.5 1.b SE ':;.8 2.9 2.b J.5 b.B 1.b SE J.l 2.3 2.2 0 •• '.5 1 •• S~E J.5 1.1 2.·; '.6 ~.I •• B B.b SSE 0.3 1.b 1.9 0.5 0.1 • •• 3 B.B · ) 10.6 5 J.5 1.8 3.2 2.1 0 •• : .1 B.1 10.1 S .. 1.b 2.b 1.8 0.3 0.1 b.9 55. ).3 I •• •• 5 5 •• 1.B ) .2 13.1 13•• 55. J.3 I.' 3.9 3.1 0.9 0.1 10.3 12.2 s. J .3 1.1 •• 0 5.b 3.8 c•• 15.1 15.3 S. 0.3 I.' ••• 5.9 3.2 0.5 16.0 I',' .. ~ .. J .1 0 •• 1.5 1.1 C., :" .2 5.5 13.5 "5" 0.3 1.3 2.3 2.2 0.8 0.1 b.9 12.' .. 0.1 J.b 0.8 Col 0.1 1.9 '.8 0.5 0.9 1.3 C.b 0.1 3•• 9.0 •~ wNW 0.3 J.B J.b 1.1 b.5 .. .. 0.3 0.8 0.9 0.2 · 2.2 1.8 ~ · ~. .. 0.3 J.b 0.1 ).1 l.b 1.3 0.3 0.9 1.3 0.3 2.9 a.b ~.7· ~H ~~. :J.2 J.b C•• 0.1 2.5 10.1 .. 0.3 o.a 1.2 I.' 0.1 3.8 10.9 CAL" 8.0 B.O CAL" a.8 a.8 TOUL 1'.5 1'.8 33.1 23.1 1 •• 1.5 ~ .1 100.0 10.2 TOTAL l'.b 20.b 3'.2 23.1 b •• 1.1 0.1 100.0 9.B

~ A • J U ~

HlJURL. 08SERYA T 10~S OF .. I~O SPEEU HOURL. OBSERY AT I O~S OF "INO SPEED "ILES PER HUUR MILES PER HOUR

I 8 13 19 25 32 39 1 a 13 19 25 32 39 TO TO• TO TO TO TO TO TO OYER AYE TO TO• TO TO TO TO TO TO OYER AYE OIR 3 1 12 18 2. 31 38 4b 4b TOTAL SPEED OIR 3 1 12 1B 24 31 3B 4b 4b TOUL SPEED

N , .4 1.3 '.b 2.1 0.1 9.1 10.b ~ 0.3 1.3 3.5 2.0 0.2 1.2 10.b NNE 0.3 1.5 3.B 1.9 0.1 1.b 10.3 NNE 0.3 3.2 1.b 0.1 b.l 10.1 HE v •• 1.1 3.9 1.9 0.1 8.0 9.9 ~E 0.2 I.'1.3 2.9 1.2 0.1 5.b 9.1 ENE ~.2 ".1 ;.9 0.2 2.0 8.1 E~E 0.2 0.5 0.1 0.1 1.b 1.1 E 10.5 J.B 0.1 0.1 2.1 b.5 E 0.3 O.b O.b 0.1 1.5 1.1 ESE 0.' 1.1 0.9 ).1 2.b 1.0 nE 0.' O.B 0.' 0.1 1. B b.2 SE u.1t 1.8 1.2 0.1 3.1 b.' SE 0.3 1.1 1.1 0.1 2.1 1.2 SSE 0.2 1.1 1.2 0.1 3.3 1.3 SSE 0.3 1.0 1.2 0.1 2.5 1.5 S e.3 1.9 3.0 0.5 • 5.1 B.5 S 0.' 2.1 303 0.9 • b.l B.l SS. 0.' 2.' 2.3 0.2 9.a 10.0 SS. 0.5 2.3 5.8 3.0 J •• • 11.9 10.b sli 0.3 2.1 b.'••• 5.5 1.1 0.1 lb. 1 12.' S.. 0 •• 2.9 8.B b.9 1.3 0.2 20.' 11.a "5.. 0.2 1.5 3.J 1.9 0 •• • 6.9 10.9 .S.. 0.3 1.9 3.b 1.8 0.2 1.9 10.1 .. v.3 1.1 1.9 0.5 0.1 3.9 9.2 • 0.3 1.b 2.3 O.b '.a a.l ..... 0.2 1.2 1.3 0.2 · 2.9 1.9 ..... 0.3 1.3 1.b C.2 · 3.5 1.1 ... 0.2 1.3 2.0 0 •• • ••0 B.5 0.3 0.9 1.5 0 •• 3.1 B.5 H". 0.2 I... 2.2 1.b 0.1 5.1 10.5 H~.".. 0.2 1.0 1.1 0.8 0.1 3.1 9.9 CALM 1 •• 1.b CALM 8•• B•• TUTAL 12.1 23.1 .1.2 20.0 2.B 0.2 100.0 9.2 TOTAL 13.' 21.9 '2.1 20.0 2 •• 0.2 100.0 9.1

From the Climatological Handbook, 1968.

15 Table 4.--cont.

J U l Y AUG U 5 T

HOURLY o~~~RVAT IONS OF wIND SPEEU HUURlY 08SERVATIONS UF WINO SPEED MileS P':A HQUR NILES PER HOUR

1 ~ 8 13 U 25 32 39 1 ~ 8 13 19 25 32 39 10 TO TO TO TO TO TO TO OVeR AVE TO TU TO TO TO TO TO TO OVER AVE olA 3 7 12 18 2~ 31 38 ~6 ~6 TUTAl SPEED olR 3 7 12 18 H 31 38 ~6 ~6 ToUl SPEED

N J.~ 1.7 ~.5 2.2 0.1 8.9 13.1 II O.~ 1.~ ~.7 1.~ 7.9 9.6 NNE 0.3 1.9 5.0 1.9 0.1 9.1 10.0 NNE 0.5 1.7 ~.2 1.6 • 8.1 9.5 NE ~.4 1.9 3.8 1.7 0.1 7.9 9.6 NE 0.7 1.8 3.~ 1.0 • 7.0 8.8 ENr u.3 J.8 0.9 ,).2 • 2.3 7.9 E..E 0.3 0.7 0.8 0.1 1.9 7.3 i a;,.3 ; ... e.1 • 1.0 5.~ E o.~ 0.9 0.3 1.7 5.3 ESE C.2 J.5 0.3 1.0 5.7 ESE O.~ 0.7 O.~ • 1.6 5.9 ~E J.3 J.8 ~.8 • 2.0 6.6 SE '.5 1.5 1.0 • 3.0 6.5 SSE 0.2 0.9 1.1 • 2.2 7.2 SSE 0.3 1.7 1.1 • 3.1 6.7 S c .4 1.7 2.7 0.5 • 5.3 8.2 S 0.8 2.2 2.9 0.3 • 6.3 7.5 S~W ,.~ 2.2 Sol 1.3 C.2 9.3 9.2 SSw '.7 2.6 ~.7 1.5 0.1 9.5 9.0 ~w J.7 3.3 8.0 3.5 ~.4 16.0 1C.1 SW ,).8 2.8 6.2 2.9 0.3 • 13.0 10.0 wSW :: ... 1.9 3.3 1.1 0.1 6.7 9.1 wSw '.5 1.9 3.3 1.0 0.1 • 6.7 8.9 W ~.~ 1.9 2.6 V... 0.1 5.~ 8.5 W 0.5 1.8 2.2 ,.~ • ~.8 7.9 o.~ ~.O O.~ 0.3 ~.2 8.0 WNW " .2 1.6 1.8 8.2 WNW 1.5 2.1 • ..W 0.3 1.~ 2.1 C.7 ~.5 8.7 N. 0.5 1.5 2.3 0.6 ~.9 8.~ ..NW ) .2 1.2 2.8 1.~ 5.6 10.2 ..NW O.~ 1.0 3.0 1.0 5.5 9.5 tUN 8.e 8.8 tAlN 11.0 11.0 ToUl ".3 H.3 44.9 15.6 1.J l.JC.O 8.~ ToUl 19.0 25.7 ~2.5 12.1 0.6 100.0 7.7

5 E P 7 ~ ~ 8 E R OtT 0 8 E R

HOURLY o8SERVATI0..s OF WI ..o SPEED HOURLY 08 SERV AT I O"S OF WI ..o SPEED IIILES PER HOUR NILES PER HOUR

1 ~ 8 13 19 25 32 39 1 ~ 8 13 19 15 32 39 TU TU TO TO TO TO TO TO OVER AYE TO TO TO TO TO TO TO TO OVER AVE UIR 3 7 12 18 2~ 31 38 ~ .. ~6 TOUL SPEEO aiR 3 7 12 18 H 31 38 ~6 ~6 TOUl SPEED .. J.7 1.8 S.:' 3.1 J.3 11.0 10.5 N 0.5 2.0 ~.~ 1.3 • 8.3 9.3 NNe '.7 1.9 5.0 2.7 0.2 10.5 10.2 "NE O.~ 2.~ ~.5 2.3 0.3 9.8 10.2 NE , .7 2.3 3.9 1.~ 0.1 8.~ 9.0 NE 0.6 2.2 2.5 0.9 0.1 6.~ 8.5 ENE ~ .3 J.6 0.6 J.1 1.6 6.8 ENE 0.3 0.7 0.6 0.1 • 1.8 7.1 E 0.5 1.3 :;.5 • 2.3 5.8 E 0.7 1.2 1.2 O.~ 0.1 3.5 7.9 ESE '.5 1.2 1.0 • 2.8 6.6 ESE 0.8 1.9 2.5 0.7 0.1 6.0 8.0 SE 0.8 1.9 2.J ~.2 ~.8 7.1 SE 0.6 2.5 3.9 0.7 • 7.7 8.3 S)E 0.7 1.5 1.~ '.1 • 3.7 6.8 SSE o.~ 1.7 2.~ 0.7 0.1 5.2 8.7 ) .1.6 1.8 3.3 0.8 0.1 6.6 8.8 5 0.5 2.2 3.8 2.8 0.8 0.1 10.3 11.1 SSW ~.~ 1.9 ~.6 2.2 ';'.3 9.5 10.~ SSW O.~ 1.~ ~.1 3.7 1.~ Ool 11.3 12.9 SW u.b 2.2 ~.~ 2.7 0.6 J.1 10.6 10.6 SW 0.2 1.0 2.6 3.3 1.3 0.2 8.6 13.3 WSw 0.5 1.J 1.~ ':.6 0.1 • 3.7 9.0 WSW 0.1 0.7 1.1 0.6 0.3 • 2.7 11.1 W 0.1 1.2 1.2 J.3 • 2.9 7.7 W 0.3 0.5 0.6 Col • 1.5 7.6 WNW o.~ 1.2 0.8 '.1 2.5 6.6 WNW '.2 0.7 0.6 • 1.6 6.8 NW 0.1 l.~ 1.' -:'.2 2.5 7.' NW 0.3 0.7 0.7 0.1 • 1.8 7.3 NNW .1.3 I.e 2.1 1.1 0.1 ~.6 9.9 NNW 0.2 0.7 1.2 o.~ 0.1 2.6 9.1 tAlII 11.9 11.9 tAlII 10.9 10.9 TOUl 20.1 23... 3~.' 15.5 1.8 0.2 100.0 8.1 TOUl ll.~ 22.5 36.7 18.2 ~.7 0.6 100.0 8.9

~ a V E ~ 8 E A OEtEM8ER

Hl;UAlY C8SEAVAT ICNS OF W'''O SPEEO HoUAl Y 08SERVATTONS CF WI"O SPEEO ~ILES PEA ~UUA MILES PER ~DUR

1 ~ 8 13 19 25 32 39 1 ~ 8 13 19 25 32 39 TO TU 10 TO TO TO TO TO UVEA AVE 10 TO TO TO TO TO TO TO DVEA AVE UIA 3 7 12 18 2~ 31 38 ~6 ~6 ToUl SPEEO OIR 3 7 12 18 2~ 31 38 ~6 ~6 TOUl SPEED II 'J.' 1.2 J.a I.e e.3 • 6.8 10.6 .. 0.2 0.9 1.5 0.9 0.2 3.8 10.3 ....E J.~ 1.~ 3.0 l.J .) .1 ;.1 7.0 1C.3 ....E 0.3 ).9 2.~ 1.9 0.3 '.8 11.0 .;E vol 1.1 1.8 J.9 • ~.1 9.~ "E 0.3 1.' 1.5 0.6 • 3.~ 8.9 E"E 0.3 ,.6 :l.T j.2 1.7 7.7 ENE 0.2 0.6 0.3 0.1 • 1.3 7.6 [ J.B 1.~ 1.~ J.~ ~.O 7.3 E 0.8 1.~ 1.5 0.8 0.2 ~.7 8. , ESE J.8 2.1' 3.6 1.3 0.2 7.9 9.1 ESE 0.7 2.(' 3.5 2.1 0.3 8.5 10.0 SE 0.8 3.5 5.2 1.~ 0 .. 1 11.0 8.5 SE 0.6 3.3 ~.~ 1.6 0.1 10.1 8.9 SSE J.~ 2.,) 2.8 1.) 0.1 6.5 8.8 SSE o.~ 1.7 3.0 1.1 001 6.~ 9.3 S J.5 1.9 3.6 2.9 0.8 c.2 J •.1 9.9 11.' 5 0.5 2.2 ~.~ ~.~ 1.~ 0.3 13.2 12.3 ))w '-.1.4 1.) 2.7 3.7 1.9 :".4 10.1 ...C SS. 0.2 1.2 3.9 6.5 3.~ 0.8 0.1 16.1 15.1 SW J.3 1.1 2.3 J.2 1.9 0.6 0.1 9.5 1~.6 SW o.~ 1.0 3.0 3.9 3.1 1.1 0.2 12.6 1'.7 WSW 0.3 J." 0.7 '.6 o.~ ).1 • 2.7 12.3 wSw 0.1 0.2 0.5 0.6 0.2 0.2 • 1.7 13.7 W O,J ,.~ ":.3 0.1 • 1.0 7.C W 0.2 0.3 0.2 001 • • 0.8 8.6 w..w 0.2 J.3 J.2 • 0.7 5.9 W... 0.1 0.1 0.1 O.~ 6.~ N. 0.2 ':'.4 C.~ 0.1 ) .1 1.2 8.8 Nw 0.1 VIOl J.1 O.~ 7.6 ..Nw J.3 J.5 O.T ·J.1 • 1.7 8.1 NNW 0.1 0.2 0.2 C.1 0.7 8.8 CALli ; ".0 CalM 10.2 10.2 ... 15.~ ll.~ 3C.6 2~. 9.3 2.~ 100.0 10.6 TOUl .21.", 19.5 32.3 19.6 6.J 1.5 C.2 100.0 9.1 TOUl T 0.3

16 U Q.l ~ 0 ~-lJ-'~--Ii-~-HJl--!H--,J--JH!-.WH'~---t-t-b't E

S -20 ~~""""'T~""""i"li'i'",'" SEPT 75 OCT NOV

N 20 r------~---~--~----I

U Q.l ~O E

N 20 .,.------~--~---____r ~Iv, u Q) -I-h-~~~+J-+-_II_+'.\_____+.l,._jUJj~Ii4!_~Ithtt_l__J+rlI_\h_t_:___ttttHf!ttH_++.+~ \ iLi ~ 0 ,(: J I:i I E I ~ f ~ ~, S -20 , iii iii iii iii ii' ii' iii iii ii' , iii iii iii ii' iii iii' iii iii i , , i , i , iii i" i , iii i i rrrrrJ MAR APR MAy

N 12...------__-----..

u Q) ~ 0 +f-:l+-fIflHHl--Il+:-H-I-lJI-II+l+-+----H+++JI.4hI--+lIh--I-:-+J+\jH E

JUNE JULY AUG

Figure 8a. One-year time series of the N-S wind component for West Point. For this chart a positive north component means the wind is from the

south (Cannon and Laird t 1978).

17 WESTPTWINWX**** 47 40N-122-23W 2.9 WESTPTWINWX**** 47 40N-122-23W 2.9

s 82 DAYSSTARTINb 753350400 10 DOF~ s I 82 DAYSSTARTING753350400 10 OOF Nt-< I I I IN-< -0 I I I 1-0S

~ ~ S .s S S -< -< If) If)

S S ~+\ CD CD +~

0 0 a- a- u u ~ ...... S UN> -0 ~+ \1\1 \ +~ I-' U U co Z z a: a: t-f t-f a: a: a:s S ~t >.q .q , \ +~

~ .S S .S N N -< -<

lS0-.00 0·.50 1. 00 1. 50 2-."0 ~'.00 0.50 L 00 L50 t."0 CYCLES/DAY CYCLES/DAY V-COMPONENT WINTER U-COMPONENT

Figure 8b. Frequency spectra for the north (v) and east (u) component of wind for West Point during winter (December-February) (Cannon and Laird, 1978). WESTPTWINWX •••• 47 40N-122-23W 2.9 WESTPTWINWX •••• 47 40N-122-23W 2.9

82 DAYSSTAATING761530400 10 DDF 82 DAYSSTARTING 761530400 10 DDF ~I I I I l~ ~I I I I I~

lSI lSI lSI lSI If) If) If) 'If)

lSI lSI ..q ..q ~+I\II +~

0 0 0- 0- U U ...... lSI lSI lJ..J(1") ~+ +~ ~ en \I\ ~ u U Z Z a: a: ...... a: a: CI:tg lSI >N N ~+ I A I\ +~

lSI ,lSI lSI lSI ......

lSl0".00 0.50 L 00 1.50 2"."0 ~.00 0.50 L 00 1.50 2."0 CYCLES/DAY CYCLES/DAY V-COMPONENT SUMMER U-COMPONENT

Figure 8c. Frequency spectra for the north (v) and east (u) component of wind for West Point during summer(June-August) (Cannon and Laird. 1978). WEST POINT WIND-WAVE ROSE

MAXIMUM STORM CONDITIONS Hs =4.3-----_____ ~TS'4.4

Me~I~~!MS~TOR(;MCONDITIONS

T?4.2

MAXIMUM STORM CONDITIONS PERCENT OCCURANCE Hs =4.1 2 4 6 8 10 12 Ts =4.1 )

MAXIMUM STORM CONDITIONS-I1--- Hs =4.9 ~ Ts =4.6 MAXIMUM STORM CONDITIONS Hs =6.0 _____ Ts =5.0 PERCENT CALM 16.3 LEGEND CHARACTERISTIC WAVE Hs (ft) Ts (sec) UP TO 1.0,Ts =2.0 ,., , ..::.., Hs=1.0, Ts=2.0 TO Hs=2.5, Ts=3.5 OVER Hs=2.5, Ts=3.5

Figure 9. Annual wave climatology computed for West Point from the wind climatology at SEATAC (Skjelbreia, 1981).

20 Suspended particulate concentrations in the air over the industrialized Duwamish Valley and the tide flats of Tacoma have regularly exceeded estab lished local and national standards since monitoring was initiated (Table 5 and Fig. 10). The long-term trend in suspended particulate concentrations over the region decreased until 1976 and then leveled off or increased slightly from 1976 to 1979. Increases in particulates were observed in both industrial and suburban residential areas in 1979, with seven stations exceeding the national standard of 75 ~g m- 3. Monthly averages above 160 ~g m- 3 have been measured in the two major industrialized areas. Of the stations monitoring ozone concentrations, four of ten in 1978 and seven of nine in 1979 measured levels that exceeded national standards. Ozone concentrations are higher in summer months due to more hours of sunlight per day, with maximum concentration normally occurring 10-30 krn southeast of major urban centers. Of the stations monitoring CO concentrations, ten of twelve in 1978 and nine of thirteen in 1979 reported levels that on at least two occasions ex ceeded an 8-hour average of 9 ppm, the national ?tandard. High ambient levels of CO occur near congested areas where there is slow-moving motor vehicle traffic and when low-level winds are light and stable meteorological conditions exist.

Table 5.--Annual average concentration of suspended particulatesl for stations in the Puget Sound region 1972-1979*

Year Everett Duwamish Tacoma Auburn

1972 60 97 94 55 1973 53 111 82 63 1974 40 77 69 51 1975 36 66 54 38 1976 45 83 87 49 1977 43 94 91 54 1978 45 100 98 54 1979 50 101 107 62

l(~g m- 3). *(Puget Sound Air Pollution Control Agency, 1972-1980).

21 SDlJl17'---+--~---.:--r--'--+-_""'""'----._---.::--'--+---+----+----t-----c_--+---+----+----t--_------tPUGET SOUND RIR POLLUTION CONTROL RGENCY

SUSPENDED PRRTICULRTES 1980 RNNURL GEOMETRIC MERNS (MICRClGRAMS/CU METERI

N ~

---~~~~_fQ._------KING CD

TI1 T WATER RES +10 r-- i~ ~ ~-.o ~ ---1 s 52ID.O i i i i KlTSAP CD rPiE~-Ca----- !

\' '" ., ., ., 20 , , !I2IQ.O \ . . THUAS TON CO I, PIERCE CO ""-["5 \ !I2ll5Jl+----+---t---+...::::".-t---+---+---t---+--t---+----+----+---+--t---+---+---t---+----+ mo 5Is"o S!O.O z.o D:I.D ~.D '10.0 !5It5.D !!5O,o ~ S1.O 565.D 57O.D .,.,.",0 580.0 ~.D ~ 9!l.O 600.0 &m.£J UTM (KILOMETERS ERST!

Figure 10. Mean annual particulate concentration for 1980 (Puget Sound Air Pollution Control AgencYt 1980).

22 2.6. Surface hydrology The mean annual flow for the major rivers of the Puget Sound region varies greatly with locality (Williams et a1., 1982). By far the largest input is from the northern tributaries, with the Skagit River being the largest single source (Fig. 11). There are two periods of high stream flow each year (Fig. 12). One occurs during the fall and winter, coinciding with the season of maximum pre cipitation. The other, in late spring and early summer, is caused by snow melt in the mountains, augmented by rainfall. Streams rise to near or above flood stage several times during each rainy season; the highest flood crests occur in late fall and early winter. Stream flow also shows large variability from year to year (Fig. 12b).

3. Large-scale Meteorological Characteristics Throughout the winter the synoptic (large-scale) meteorology over Puget Sound is characterized by a sequence of cyclonic (low sea-level pressure) dis turbances (Klein, 1957) that move over or to the north of the region. This sequence is interrupted infrequently by anticyclones (high sea-level pressure regions). Spring and autumn are transition periods when the frequency and intensity of cyclones diminish and increase respectively. Summer is marked by light cyclonic activity and by long periods of anticyclonic influence due to the intrusion of a high-pressure region from the north Pacific. Winter cyclone tracks for the Northeast Pacific indicate that most of the air masses affecting Puget Sound have their origin in the central Pacific. While it is difficult to generalize all synoptic weather charts, two typical storm types suggest themselves (Reed, 1932). In the first type, designated Ll (Fig. 13a), pressure patterns are associated with a large and extensive low-pressure area in the Gulf of Alaska and a series of accompanying cold frontal systems. The center of the low pressure usually drifts slowly, whereas the frontal systems advect rapidly across the Pacific, rotating about the center of the low. The warm sector ahead of the front is usually of small extent by the time it is in the vicinity of the coast; therefore, classical warm fronts are often weak and diffuse although they are still associated with stable air masses. As the storms approach the coast, they are modified by the effect of the continent (Lau, 1979). The surface features of the cold front in Ll often rapidly approach the coast and slow, while higher level features continue to move over Puget Sound. The severity of the weather associated with the front is not always as great as it is when the storm system is over the Pacific. Thus, it is often difficult to forecast the timing and severity of frontal features over Puget Sound by extrapolating the speed of the storm while it is over the Pacific. The CYCLES project is an extensive study of the meso scale and microsca1e organization and structure of clouds and precipitation in storms affecting western Washington (Hobbs, 1978; Hobbs et a1., 1980; Parsons and Hobbs, 1982).

23 48 0

47 0

124 0 1230 1220 3 Figure 11. Meanannual runoff (m s-l) for Puget Sound. Periods of record vary (Williams et al. t 1982). MEAN MONTHLY RUNOFF

1400

1200

1000

lJ) ...... 800 l""l E LL LL 0z 600 :::::l 0::

SUM 400 /----, ~--\ /' / \ / " // \ / - / \ SKAGIT / \ / ---- \ 200 / '\. '\. ~------... _------...... " SNOHOMISH ...------" '--- .-- '--",------. PUYALLUP O-+----.---....-----r---..,.------,-----, OCT DEC FEB APR JUN AUG SEP MONTH

Figure 12a. Mean annual cycle of discharge for Puget Sound's three major tributaries (Williams et al., 1982). The period of record for the Skagit was 1941-1979, the period for the Snohomish was 1963-1979, and the period for the Puyallup was 1914-1979.

25 ANNUAL RUNOFF 1200

1000

800

lJ) ~ -E SUM N LL 600 0'\ LLo Z :::> 0:: 400 SKAGIT //'\ y /' /" /' \ /', / \ --- / \ .../\ /' '" -- / \ / "' \ \/ \/ /' ' .... "'-- '-'-v/ SNOHOMISH 200 - // v v

----- ...... ~~~------_.-~...."" , ",'-~-._--.--.- - """, -'~~---- - PUYALLUP ...... _-""'- ..., ...... -- o I I II I I I II 64 66 68 70 72 74 76 78 79 YEAR

Figure 12b. Interannual variability of discharge for Puget Sound1s three major tributaries (Williams et al., 1982). .~. ~~

a b

.~ .~-

.... d

Figure 13. Typical weather patterns affecting the Pacific Northwest a) Ll, b) L2, c) HI, d) H2 (Maunder, 1968; Overland, 1981).

27 In the second type of storm, L2 (Fig. 13b), small disturbances form in the central Pacific and move across the Pacific on a northeast trajectory, commonly passing parallel to the coastline or crossing over British Columbia. Such systems can rapidly intensify as they propagate north, seaward of the coastline, and produce some of the most severe P~get Sound weather, such as the Columbus Day storm in 1962 (Lynott and Cramer, 1966). A subset of this type ll is small synoptic-scale cyclones or II vortices " that form in the western Pacific behind major frontal bands such as Ll (Reed, 1979; Mullen, 1979; Locatelli et al., 1982). At some time during most winters an upper-level blocking ridge of high pressure will develop over northwest Canada, accompanied by high pressure over the Puget Sound region, HI (Fig. 13c). As a result, there are clear skies due to air mass subsidence induced by the high-pressure area, near freezing temperatures, and very stable air in the surface layer of the atmos phere (Overland and Walter, 1981). The summer season in Puget Sound is influenced by marine air from the Pacific moving over the region by way of the Strait of Juan de Fuca (Mass, 1982). From the end of June through August the synoptic situation is char acterized by a marine high-pressure system influencing the area, H2 (Fig. 13d). This high-pressure influence leads to a dry season with many clear days, warm temperatures, and prevailing winds from the west to northwest. Cyclonic disturbances may still occur, but their severity is greatly lessened and their frequency is likewise diminished compared to winter. The spring season is not significantly different from winter except that temperatures are higher due to increased insolation; the frequency of cyclonic disturbances decreases, and their distribution over time is irregular. The strength of the upper-level flow diminishes in intensity as spring progresses. Autumn is another transition period. A common characteristic of early autumn is the continuing influence of the Pacific high-pressure system in the area. The high-pressure ridge eventually breaks down, shifting the prevail ing winds to southwesterly and strengthening the upper-level flow. With this shift come the cyclones and fronts associated with winter. The frequency of occurrence of these major map types is summarized by Table 6 derived from Maunder (1968). During winter months, December through February, lows predominate over highs by 3:1; type Ll forms 62% of the observed lows. By contrast, for the summer months, July through September, type H2 dominates on 48% of the days. Further discussion of typical synoptic weather situations for western Washington is given in Halladay (1970).

28 Table 6.--Number of days per month with synoptic weather patterns L1, L2, HI, H2*

Weather Month pattern JF MAM JJ A S 0 N 0 YEAR

L1 14 10 7 12 7 4 5 5 5 14 10 13 106

L2 9 4 11 10 6 6 4 7 6 4 13 11 91

HI 4 2 3 0 1 1 1 1 3 6 3 4 29

H2 3 14 8 7 13 15 16 14 16 5 2 3 116

*Adapted from Maunder, 1968.

29 4. Regional Meteorological Phenomena 4.1. Overview Regional weather phenomena are the result of the superposition of forcing on synoptic (1000 km), meso- (50 km), and local (5 km) scales. The inter action of synoptic-scale weather patterns and the topography of the region determines mesoscale and local meteorological features. For example, the Olympic Mountains affect wind and precipitation patterns because air mass stability confines airflow to the low-level marine channels, the N-S-oriented Cascade Mountains have a blocking effect on large-scale weather systems, and the proximity of the inland waters to the Pacific Ocean to the west and the highlands to the east of Puget Sound produces a strong diurnal variation of the summer wind pattern due to generation of land and sea breezes and valley winds. The mountains restrict the free movement of air at sea level, which prevents geostrophic adjustment between pressure and wind, so that the earth's rotation has little effect on the direction of the wind; winds blow predom inantly from high- to low-pressure in a direction dictated by the orientation of the low-level channels. Since Puget Sound is oriented at approximately a right angle to the Strait of Juan de Fuca, high pressure to the east gives easterly (i.e., down-gradient) winds in the Strait of Juan de Fuca and light winds in Puget Sound, while low pressure to the north gives strong southerly winds in Puget Sound and light winds in the central part of the Strait of Juan de Fuca. Wind speed (in knots) for the Strait of Juan de Fuca is roughly ten times the difference in the sea-level pressure (in millibars) at Bellingham and Quillayute; the wind speed for Puget Sound is roughly ten times the dif ference in pressure at Olympia and Bellingham (R. Anderson, personal communi cation; Overland, 1981). Because of the different orientation of Puget Sound and the Strait of Juan de Fuca, a frontal passage can lead to differing time sequences of winds in the two regions (Church, 1938). For a typical example (Fig. 14), at 0500 Pacific Daylight Time (PDT), the lowest sea-level pressure is at the coast, which creates east winds in the Strait of Juan de Fuca. By 1100 PDT, the front has passed over the inland waters, and pressures are beginning to in crease to the south behind the front giving rise to southerly winds in Puget Sound. By 1700 PDT, the front has passed to the northeast of Bellingham, and pressures have increased at the coast reversing the wind direction to westerly in the Strait of Juan de Fuca. Thus, the winds in Puget Sound have increased and then decreased from the south during the frontal passage, while the wind direction in the Strait of Juan de Fuca has reversed from east to west. The following sections review studies that have recently led to a consider able increase in understanding of the factors affecting the meteorology of the Puget Sound region.

30 49 0

~'~--1:'

W 48 ...... 1 I '--- QUI\ I,ovute ~,.,'" \..J' I )\,IIOYUle ~ 992mb

4r-j VJVV rU~~f: j 1100 PO]\ ,I I \ 1250 1240 I

Figure 14. Typical local wind patterns for the passage of a front through western Washington (Overland, 1981). 4.2. Gap winds and bora Several times during most winters a cold high-pressure area is es tablished east of the Cascade Mountains with a low-pressure system offshore (Fig. 15a). This situation results in a large east-west pressure gradient over the Puget Sound region and the formation of locally strong and at times destructive winds. Reed (1931) applied the term "gap winds" to the strong easterly winds observed in the Strait of Juan de Fuca under these conditions and characterized these winds as II not being, properly speaking, gradient winds in that geostrophically balanced pressure gradients are totally inadequate alone to account for the velocities observed." He defined "gap winds" as the flow of relatively homogeneous air in a sea-level channel with a source region or reservoir at one end. A component of the pressure gradient parallel to the channel causes the flow to accelerate along the channel. Reed also concluded that the high velocities in the Strait of Juan de Fuca were due to a venturi effect caused by the converging sides of the channel. In a more recent investigation of gap wind conditions, Overland and Walter (1981) combined high-resolution, low-level (50-m) wind fields derived from aircraft flights over the Straits of Juan de Fuca and Georgia with surface data and upper-air soundings. It was found that the presence of converging sides of the channel was incidental to the increased wind speeds and that acceleration due to the pressure gradient along the channel alone was suffi cient to explain the observed wind magnitudes. An example for the period 2040-2400 GMT 23 February 1980 is shown in Fig. 15b. Winds in the Strait of Georgia were light and variable where the pressure gradient was flat; in the eastern part of the Strait of Juan de Fuca the flow was generally disorganized but tended to have an easterly component. In the central and western portion of the Strait of Juan de Fuca the component of the pressure gradient along the axis of the channel remained nearly uniform, while the winds increased to 14 m s-l at the entrance to the Strait. Vertical wind speed measurements from the aircraft indicated that subsidence was occurring over the inner part of the Strait of Juan de Fuca and the Strait of Georgia, whereas vertical motion was upward west of 124°20'W. For the inland waters of Puget Sound and the Strait of Juan de Fuca, the acceleration of the wind provides the primary balance to the component of the sea-level pressure-gradient force imposed by the synoptic weather situation along the direction of the various channels. For flow at constant height the increase in wind speed due to a constant sea-level pressure gradient is given by the Bernoulli equation:

(1) where u is velocity, U is an initial velocity, ~p is the pressure difference, and p is a density. o A situation similar to 23 February occurred on 13 February 1980, but in this case the major pressure gradient was situated over southern British Columbia (Fig. 16a). The pressure gradient accelerated the cold, dry contin ental air from the interior of British Columbia through the Fraser River

32 55°

126°W 1250 1240 45°

50°

49 0

~ 40° 45°

48 0 {

Figure 15. (a) Sea-level pressure analysis 1230 for 00 GMT24 February 1980 for western b Washington (Overland and Walter t 1981).

15. (b) Local wind field on 23 February and sea-level pressure analysis for 21 GMT23 February 1980 for the Straits of Juan de Fuca and Georgia (Overland and Walter t 1981). Flight level wind measurements are shown as small wind arrows. Bold arrows with circles indicate surface station or buoy reports. Wind convention is in knots. The heavy dashed line at the entrance to the Strait of Juan de Fuca represents a transition from subsidence on the north and east side to positive vertical motion seaward of the line. 140° 135° 130° 125° ._- 126°W 125° 124° 123° 122° ! I ~16 lIiiJi. 50°

55° 49.N1 / 'UU,~~'" ".. r. r4~ O~ '-0. r _:;--~

1008 .• III .\ \~ ...... <. _ • 090 45°

W 50° +=-

48 48°1 l?' 'l~~1;t-r ° 40° 45°

40° 4?O 4?O

125° 120° 115° 126° 124° 123° 122°

a b

Figure 16. (a) Sea-level pressure analysis for 00 GMT14 February 1980 (Overland and

Walter t 1981). (b) Local wind field on 13 February 1980 and sea-level pressure analysis

for 21 GMT13 February 1980 (Overland and Walter t 1981). 126°W 1250 1240 123 0 1220

49°N 49"

480 480

2100 GMT 13 FEB 80

47·- 470

0 126 1250 1240 1230 1220

Figure 16. (c) Wind and dewpoint fields from surface and aircraft reports 21-24 GMT 13 February 1980 (Overland and Walter t 1981).

35 Valley near Vancouver (Fig. 16b). This dry air displaced the more moist, marine air as it flowed across Georgia Strait and was ultimately channelled out the Strait of Juan de Fuca (Faulkner, 1980). The change of dewpoint temperature marked the air mass boundaries (Fig. 16c). The dry air maintained an essentially constant velocity while spreading laterally and growing in depth, as shown by a downstream increase in inversion height. The momentum contained in the jet increased with downstream distance due to the presence of a pressure gradient along the flow direction. The eddy-like feature beyond the entrance to the Strait of Juan de Fuca, which had light SE winds to the west of its boundary and strong (10-12 m s-l) winds from the E to the east of the boundary, may have been due to the presence of a hydraulic jump. Vertical wind speeds as recorded by the aircraft were downward at 1 ms-1 on the east side and upward at 0.4 ms-1 on the west side of the boundary. Another response of the flow in Puget Sound to pressure differences is the creation of a downslope wind called a bora, which blows out of the passes in the Cascade Range when high pressure exists to the east of the mountains. Since the source region for the air in eastern Washington is often very cold, the adiabatic heating of the air upon descent out of the passes is not suf ficient to raise the temperature to levels equal to ambient conditions in the Puget Sound Basin, so the cold air spreads out over the lowlands. Reed (1981) discussed a windstorm that led to a bora-like flow in Stampede Pass and gap winds in the Columbia River Gorge. Figure 17 shows the extremely large gradient of sea-level pressure in the vicinity of the Cascades for 28 Novem- ber 1979. This gradient was for the most part fictitious, merely indicating that the mountain barrier sustained a large pressure difference between the cold air in central and eastern Washington and the warm air over western Washington. An E-W cross section (Fig. 18) of potential temperature across the State of Washington from Spokane (GEG) to Quillayute (UIL) showed the intense horizontal temperature gradient that developed over and to the lee of the mountains as the upper-level inversion tilted and lowered in the subsiding airflow. Rewriting (1) using pressure coordinates gives: aD g ax ax , (2) where g is gravity, D is the geopotential height deviation from the standard value for a particular pressure level and ax is the difference in horizontal distance between the end points of the trajectory. Calculations using Eq. (1) in the Columbia River Gorge and Eq. (2) for flow in the lee of Stampede Pass estimated sufficient wind magnitudes to account for those observed.

4.3. Orographic low-pressure formation in the lee of the Olympic Mountains During the winter (December-February), synoptic weather patterns give rise to S-SW flow conditions over the Puget Sound region 75% of the time. When synoptic-scale winds are from the south-to-southwest, the Olympic Moun tains can induce the formation of a low-pressure area directly in the lee· of the mountains over Puget Sound or the Strait of Juan de Fuca (Overland et al., 1979), and Vancouver Island can induce low pressures over the Strait of

36 of

)

right

454

intervals to 44

\ .

. \

-07 \ : --l at

(mb)

-I~

drawn

1------

are

pressure

-~~

a.~

and

487

------_--:------

( I Isobars 0 ____

_80458

--- _~

-06

l 120 \ i \@

+ f

station

484

~E"TI _?;-o470

1979.

-08

\\ left

November to

GMT

'\0>~ plotted

"" 40424446

map,

(Oe)

1981).

Surface

/25

~R\.A

(Reed,

17. Temperature

50° mb.

station Figure 2

-....I W mb 500

600L 3/0

700 4 w 00 800

900 ~ 280~~-- 1000 ---

UIL 100 km

Figure 18. Cross section of potential temperature (OK) across the state

t of Washington (Reed 1981). Station UIL is Quillayute t SEAis Seattle and GEGis Spokane. t Georgia (Myers, 1966). The importance of the presence of such a low-pressure area was dramatically demonstrated on 13 February 1979 when the Hood Canal Bridge sank ~uring surface winds in excess of 50 m s-l. Reed (1980), who analyzed the meteorological conditions for this event, found that although the gradient of sea-level pressure at the bridge was strong due to the synoptic pressure gradient, it was greatly enhanced by the formation of a mesoscale low-pressure area in the lee of the Olympics (Fig. 19). In the restricted channels of Puget Sound the air flow at the surface accelerated toward the low pressure producing the observed high wind speeds. In contrast, Walter and Overland (1982) made measurements with the NOAA P-3 aircraft on three days during S-SW conditions in February and March 1980 (Fig. 20a-f) and found a region of light wind speed and flat pressure gradient in the lee of the Olympic Mountains and only slight troughing in the pressure field over the eastern Strait of Juan de Fuca. To explain this difference one needs to consider a non-dimensional number, the internal Froude number, F, which compares the momentum of the incident flow to the stratification of the flow. This number is the critical parameter in determining whether the upstream air will go over (large F) or around (small F) an isolated obstacle such as the Olympic Mountains. For a fluid having continuous stratification the Froude number is given by -V F - hN ' (3) e where V is upstream flow velocity, h is the height of the mountain, and N is the stratification parameter, the BrUnt-Vaisala frequency, e

N 2 =9.- dSe (4) e Se dz' where g is gravity, Se is the equivalent potential temperature, and z is the vertical coordinate. The vertical derivative of equivalent potential tempera ture accounts for stratification due to moisture as well as ambient temperature. On the three days discussed by Walter and Overland (1982), the boundary layer was slightly stable throughout its depth with the internal Froude number in the range F = 1.0-1.4. For the Hood Canal Bridge storm a smaller value of N together with high upstream winds led to a calculated value for F of 4.6. e For strong relative stratification, the primary flow about an obstacle is in quasi-horizontal planes (Fig. 21a and b) where the flow in each plane is given by a two-dimensional potential solution defined by the contour of the terrain at that level (Drazin, 1961; Riley et al., 1976; Hunt and Snyder, 1980). Small vertical displacements of the streamlines passing around the side of the obstacle are due to the need for the potential energy to decrease in order to balance the increase in kinetic energy of the flow around the obstacle. Although the Froude numbers for the low wind studies in Walter and Overland (1982) were in the range of 1.0-1.4, the pressure and wind fields (Figs. 20 b,d,f) show qualitative agreement with experimental results for

39 Figure 19. Regional surface map for 12 GMT 13 February 1979 (after Reed, 1980). Isobars are drawn at one millibar intervals (dashed at higher elevations). Winds are in knots. Maximum gusts (G) at observation time and in preceding hour are plotted below stations.

40 126°W 125° 124° 123° 122°

49°N 49°

+::> ......

48° 48°

40°

47 0

0 0 115° 1260 1250 1240 123 122 a b

Fig. 20. (a) Sea-level pressure analysis for 00 GMT19 February 1980 and (b) mesoscale wind and pressure field at 21 GMT18 February 1980. 1250 1200 126°W 125 0 1240 1230 122 0 / ._ II

49°N 490

45 0

~ N

48 0 48 0

40 0 0 47 47 0

0 c d l260 125 1240 123 0 1220

Fig. 20. Cc) Sea-level pressure analysis at 00 GMT29 February 1980 and Cd) mesoscale wind and pressure field at 21 GMT28 February 1980. 126°W 1250 1240 1230 1220

550 49°N 490

1019

-1=>0 1020 W 1021 48 0 1022- I 48 0

40 0

47 0 47 0

1150 1260 1250 1240 0 0 e f 123 122

Figure 20. (e) Sea-level pressure analysis at 00 GMT10 March1980 and (f) mesoscale wind and pressure field at 21 GMT9 March1980. ~.",.~-:$"-~--:~~,- ~------.... \ '--: £ -- ~.(

--~ ---

.j:::> .j:::>

--' .... -:~ ....

Figure 21a. Plumes from upwind stacks at various elevations (Hunt and Snyder, 1980). Top is for F = 0.2. Flow is constrained to move principally in horizontal planes. A slight hydraulic jump occurs just downstream from the top of the hill. Bottom is for F =0.4. Here the flow is able to move farther in the vertical direction, and the region where the flow goes over the top is broader. Flow going over the top separates half-way down the lee slope. Numerical Results

~ Experimenta I Results u •

~ - -:;...... "'.•_;,.I~!:-••r:,~..._.,.,•. ...,·,.,.·..,.·.._·,,··

t:; --,~;;:Y/8:1" / --L 10

,.. 50 40 30 o X1(cm)

Figure 21b. Comparison of experimental and analytically computed (Drazin t 1961)t streak lines in the horizontal plane at mid-level of a Gaussian-shaped obstacle for a Froude number of 0.154 (Riley et al. t 1976). low Froude number flow. However, from the magnitude of the isotherm displace ment in cross-section plots of constant e surfaces along the east side and in the lee of the Olympics, it was evident that the flow was approaching the transition region between small and large Froude number theory. For the case where F » 1, Smith (1980) developed a hydrostatic linear model for stratified flow over an isolated mountain. His results for a bell shaped mountain showed an asymmetric perturbation surface pressure field with high pressure over the windward slope and low pressure on the lee side. This pressure distribution caused the surface streamlines to be deflected around the sides of the mountain and to maintain a permanent outward deflection downstream. Horizontal divergence in the lee of the mountain caused a sinking of warm air from aloft and a decrease in the vertical distances between down wind, low-level, constant-density surfaces. When this perturbation pressure field is added to the background synoptic-scale pressure field (Smith, 1981; Fig. 22), the result is in agreement with the sea-level pressure analysis for parameters from the Hood Canal storm (Fig. 19). Reed (1980) indicated that in the vicinity of the Hood Canal Bridge on 13 February 1979 the pressure gradient was a maximum of 6 mb in 15 km or 0.4 mbkm-1. Comparison of the observed winds at the time of the bridge col lapse (from Reed, 1980, Table 2) with those calculated for a confined channel from Eq. (1) and a value of the pressure gradient of 0.4 mb km- 1 shows good agreement (Table 7). When the internal Froude number has a value on the order of 0.5-1.5, the flow response in the lee of the Olympics will be relatively benign with light and variable winds. However, when the Froude number is of order 4-5, a closed mesoscale low-pressure region will be induced in the lee of the mountains. The flow at the surface in the restricted channels of Puget Sound responds by a rapid acceleration toward low pressure to give extreme wind speeds in a localized area.

4.4. Effects of orography on precipitation--the Puget Sound convergence zone The surrounding mountains not only have a strong effect on the wind fields but also on the precipitation patterns in Puget Sound as shown by Mass (1981) and Parsons and Hobbs (1982). In the spring transition months (April June), when high pressure builds northward into the eastern Pacific Ocean, the coastal winds change from a predominantly southerly to a northwesterly direc tion. As southerly winds veer to the northwest after a frontal passage at the coast, there is a narrow range of wind directions and speeds (Fig. 23) where the air will simultaneously flow eastward both north and south of the Olympic Mountains. This flow pattern results in the formation of an area of con vergence over Puget Sound (Fig. 24). Mass (1981) studied 25 cases of this convergence phenomenon and concluded that the controlling parameters were the wind direction and speed on the Washington coast, although most convergence zone events were also associated with weak atmospheric stability typical of spring. He found that a convergence event was most likely to occur when, for four continuous hours, the Hoquiam wind direction was between 260 0 and 320 0 and the wind speed ranged from 2 to 7 m s-l. AlthoUgh convergence events can occur any time of the year, they are most probable from April to June when two to four major events per month are expected.

46 ------4 -3 -2 -I ~ -...... J o I 2 3 ------4mb o 50 100km , , I

Figure 22. Sumof the perturbation pressure field from Smith's hydrostatic linear model and a hypothetical synoptic pressure field (Smith, 1981). Table 7.--Comparison of winds reported by Reed (1980) in Hood Canal 14-15 GMT 13 February 1979 and those calculated from Eq.1*

Observed Calculated Bridge 40 m s-1 40.5 m s-l 9.25 km SSW 30 33 18.5 km SSW 22.5 22.5 (assumed)

*Initial velocity used for the calculation is 22.5 ms-l.

48 N 36

8\ S

Figure 23. Polar representation of the wind speed and direction at Hoquiam, Washington, during ten convergence zone events (Mass, 1981).

49 \.\

IMay 2,1978 [May 2-:1978 1900GMT l?.QOOGMT

May 2,/9781 2100G~T I

Figure 24. Streamlines over the Puget Sound area during the con vergence zone event of May 2-3, 1978 (Mass, 1981). The position of the surface convergence line is indicated by a dashed line.

50 A composite vertical structure of the convergence zone was constructed by Mass (1981), who indicated that it is similar to that of a classical front. Northerly winds enter Puget Sound and propagate as a wedge into the pre-exist ing southerly winds (Fig. 25). The windshift line separating the opposing flows slopes upward to the north. Enhanced clearing is observed both north and south of the main convergence zone cloud band. Mass (1981) indicated that the clear area north of the zone is due to subsidence associated with the surface divergence created as air flow in the eastern Strait of Juan de Fuca splits and moves both north into the Strait of Georgia and south into Puget Sound. The clear region to the south of the zone is due to subsidence of air in the mesoscale circulation set up above the convergence line. The presence of the convergence zone has pronounced effects on the cloud iness, temperature, and precipitation patterns over the region, and its effects can be seen in Figures 26 a-c, which are composites of these parameters for the cases studied by Mass (1981) plotted with reference to the location of the convergence line. Most of these convergence events showed a band of clouds across central and northern P~get Sound with the southern boundary close to the windshift line. These clouds were generally shallow, with tops between 1500 and 2500 m in the central Sound and 3000 m near the mountains. The lowest cloud deck in the Sound frequently reached to the ground. The effect of the convergence zone on precipitation can be seen in the long-term climatology. Mass (1981) constructed a N-S cross section of monthly precipitation for Puget Sound (Fig. 27). There is a normal annual cycle at all stations except in the northern Sound where there was sustained precipita tion through May and June caused by convergence zone precipitation. Parsons and Hobbs (1983) studied the effects of orographic features in the Puget Sound region on mesoscale structures and precipitation processes in different types of rainbands embedded in synoptic-scale storms as they pass across the region. They studied warm-frontal, warm-sector, narrow and wide cold-frontal, and post-frontal rainbands and found that the influence of orography was dependent on the rainband type, the size of the orographic feature, and the airflow. Figure 28 shows that a large percentage of precip itation from warm-sector (i.e., pre-frontal) rainbands occurs at three coastal stations due to slight lifting of the airmass and from post-frontal rainbands at three stations about 100 km inland, where precipitation is considerably enhanced over the windward slopes of the Cascades. Local airflow convergence caused by the restricted flow in channels of the Puget Sound Basin also played an important role in enhanced post-frontal precipitation.

4.5. Diurnal wind variations--the sea breeze and valley breeze In the warm months of the year the wind field shows a strong diurnal var iation that is related to differential heating between the land and adjacent waters and heating on the mountain slopes. Staley (1957) presents hodographs- plots of the rotation of wind vector end points with time of day (Fig. 29)-- for July 1950, where resultant winds were derived by averaging components of the wind observed at each hour during the day over a month. In the Strait of Juan de Fuca, Port Angeles showed W-NW flow and counterclockwise rotation while Victoria showed southerly and southwesterly flow with clockwise rotation.

51 800-1 6 ...... -.... ~ ...... I- ...... r w w 850~ I ~ l.1...... r4~ ..c \ Cf) E , 0 <.T1 " t " N 9°°1 , I z I 2<{ J \ I Cf) 950~ .- ...... -... ',\ :J ". /' 0 '" :::r: ...... ~ ..- t- 1000 .- • ...... " """ a Clear Cloudy I Cleo r N Surface S Convergence Line

Figure 25. Schematic view of the low-level flow during a convergence event (Mass, 1981). LOWEST DECK 20

~ u w o o ~ o ...J U 10 t- Cf) W ~ o ...J U. o a:: w o'----J'--:8::-'-:7::-'--=-6-'--=-5-'-4~3-'---:-2...L-1--L...:0--'---_-1L_2,,---1-_3,,---1-_4--L._-=-5...L_-...L_---'-----'_8 a CD 6 7 ~ ~ COMPOSITE ZONE RELATIVE TO CONVERGENCE ZONE z

TEMPERATURE COMPOSITE u. ~ z 3- - r- o - r- t- 2 r- « > I ~ 0 ~ -I ; -2 - ~ -3 w f-- ~ -4 -'-- w b t- 4 3 2 I 0 -I -2 -3 -4 N COMPOSITE ZONE S

Cf) t Z W > 40 w z 9 30 t-« t- ~ 20 u w a:: a. 10 u. o

~ 7 6 5 4 3 2 I 0 -I 2 -3 -4 -5 -6 -7 -8 C ~ COMPOSITE ZONES Z RELATIVE TO SURFACE CONVERGENCE LINE

Figure 26. (a) Summary of the number of times the lowest cloud deck in Puget Sound occurred in each composite zone during five convergence zone events (Mass, 1981). (b) Temperature deviations (OF) from the Puget Sound mean for each composite zone (Mass, 1981). (c) Summary of the number of precipitation events that occurred in each composite zone during ten convergence zone events (Mass, 1981). 53 ,

Rain Shadow ,/ 8 \ --- N. Sound / , C. Sound ' \ , _.-.- S. Sound ,I \ , ,/ 6 • \. / , • • , • I \, ,i \ ", I. 4 , \ , ~ '\ I f' ~ ~: I" .\ " .. \.. ,/,' .~.~ I' 2 1'1 '. - \ !I.' II ". \ /:' . ,, , ~ ,

------..",.' " '":'to\ ..-,//. ' . " ---- I• .

O---,r---___.,.----r--...,.--~-r__ -___.,.-...... ,...-_r__-_r__---...I J FMAM J J A S 0 N

Figure 27. Annual variation of precipitation for the rain shadow and northern, central, and southern Puget Sound regions (Mass, 1981).

54 50 50 40 40 30 30 20 20

10 10

oL-l----l.:..:.:....:..:.Il....L.II _ LONG BEACH °CHEHALIS z WARM-SECTOR ;":'.:::; NARROW COLD-FRONTAL « .. ' .: 0:: 50 50 WIDE COLD-FRONTAL --l ~ 40 40 POST-FRONTAL o I- 30 I.J.... o .0.-'". 20 :':'~'~'~ W <.9 .... ~ 10 o...... "," Z w O...... --&o.:~ ...... U ELMA 0:: W Cl. 50

:".: ~;~:: ...... : :.... •" .1" ". o..". "0 °OLY~':~IA

Figure 28. Percentage contributions to total precipitation at three coastal stations (Long Beach, Moclips, Pt. Brown) and three inland sta tions (Chehalis, Elma, Olympia) from warm sector, narrow cold-frontal, wide cold-frontal, and post-frontal rainbands on 8 December 1976 (Parsons and Hobbs, 1982). Note the large contribution from warm-sector rainbands at the coastal stations and the large contribution from post-frontal rain bands at the inland stations.

55 VICTORIA

4.0 18

2.0

18 -2.0

PORT ANGELES

1.0 2.0 9 12 1.0 12 0 -1.5- 0 -'~D 15 21 18 21 18 1.0

EVERETT OLYMPIA SEATAC AIRPORT

Figure 29. Resultant wind hodographs for stations in the Strait of Juan de Fuca t north t central t and south Puget Sound for July 1950 (StaleYt 1957).

56 6. Acknowledgements This work is a contribution to the Marine Services Project at the Pacific Marine Environmental Laboratory. We wish to thank Robert Anderson and W. Burton of the NWS Seattle Ocean Services Unit, Don Faulkner, Steve Nikleva, and Ron McLaren of the Canadian Atmospheric Environment Service in Vancouver,. B.C., for their support and encouragement of this project. We wish to thank Drs. Peter Hobbs, Cliff Mass, Richard Reed, Ron Smith, and James Connell for their contributions and suggestions. We also thank Journal of Fluid Mechanics (Cambridge University Press) for permission to use figure 21a. We acknowledge the assistance of Professor Richard Reed, Department of Atmospheric Science, University of Washington, Seattle, Wash. 98195, in providing a copy of an unpublished manuscript by V.F. Morris titled "A study of mesoscale mountain barrier effects in western Washington and Vancouver Island."

59 7. References

Cannon, G.A. and N.P. Laird (1978): Variab"ility of currents and water prop erties from year-long observations in a fjord estuary. In: Hydrodynamics of Estuaries and Fjords, Nihoul, J.C.J. ed., Elsevier, Amsterdam, 515-535. Church, P.E. (1938): Surface details of a warm front in the Strait of Juan de Fuca. Bulletin of the American Meteorological Society, 19, 400-402. Church, P.E. (1974): Some precipitation characteristics of Seattle. Weather wise, 27:244-251. Climatolo ical Handbook Columbia River Basin States Hourl Data, Vol. 3, an, : eteoro oglca ommlttee, aCl lC ort west River Basin's Commission. Critchfield, H.J. (1978): Sunshine and solar radiation in Washington State. Office of the State Climatologist, Western Washington University, Bellingham, Washington, 98225, 38 pp. Drazin, P.G. (1961): On the steady flow of a fluid of variable density past an obstacle. Tellus, 13:239-251. Faulkner, D.A. (1980): Mesoscale observations of an outflow wind over the Southern Strait of Georgia. Pacific Region Technical Note 80-022, A.E.S., Vancouver, B.C., 6 pp. Halladay, N.E. (1970): Whidbey Island Forecaster1s Handbook, NAV WEA SERV COM INST 3140.2, U.S. Naval A,r Station, Oak Harbor, Washington, 115 pp. Hobbs, P.V., R.A. Houze, Jr., and T.J. Matejka (1975): The dynamical and microphysical structure of an occluded frontal system and its modifica tion by orography. Journal of the Atmospheric Sciences, 32:1542-1562. Hobbs, P.V. (1978): Organization and structure of clouds and precipitation on the mesoscale and microscale in cyclonic storms. Reviews of Geophysics and Space Physics, 16:741-755. Hobbs, P.V., T.J. Matejka, P.H. Herzegh, J.D. Locatelli and R.A. Houze, Jr. (1980): The mesoscale and microscale structure and organization of clouds and precipitation in mid-latitude cyclones, I: A case study of a cold front. Journal of the Atmospheric Sciences, 37:568-596. Hunt, J.C.R. and W.H. Snyder (1980): Experiments on stably and neutrally stratified flow over a model three-dimensional hill. Journal of Fluid Mechanics, 96:671-704. Klein, W.H. (1957): Principal tracks and mean frequencies of cyclones and anticyclones in the northern hemisphere. Research pa er No. 40, U.S. Weather Bureau, Washington, D.C., 60 pp. CAvailablerom7 National Weather Service, Techniques Development Laboratory, Washington, D.C. 20233.) Lau, N.C. (1979): The structure and energetics of transient disturbances in the northern hemisphere wintertime circulation. Journal of the Atmospheric Sciences, 36:982-995. Locatelli, J.P., P.V. Hobbs and J.A. Werth (1982): Mesoscale structures of vortices in polar air streams. Monthly Weather Review, 110: 14·17-1433.

60 Analysis of the pressure oscillations at several stations (Staley, 1957; Fig. 30) showed a diurnal component that reached its maximum and minimum later at Tatoosh Island on the coast than at the eastern end of the Strait of Juan de Fuca or in Puget Sound. Pressure differences between stations were greatest in the afternoon and early evening driving the westerly sea breeze, but the exact time of maximum pressure difference varied as different pairs of stations were considered. For example, the pressure difference between Port Angeles and Bellingham reached a maximum three to six hours after the maximum pressure difference between Port Angeles and Everett.

Ideally, hodographs should be elliptically shaped, rotate clockwise with time, and fall in strength during the night and increase during the day reach ing a maximum between 1330 and 1830 Local Time (LT). Superposition of other factors related to topography, mean flow field, and valley or slope winds upon the sea breeze, however, leads to distortion of this ideal shape and behavior (Mass, 1982); the existence of counterclockwise hodographs must be attributed to topographic constraints. For example, the maximum wind component toward the Cascades during the day and toward Puget Sound at night would be expected on the basis of upslope and drainage winds regardless of sea breeze. In cen tral and northern Puget Sound the winds turn clockwise on the eastern side and counterclockwise on the western side of the Sound. A similar situation exists in the Strait of Juan de Fuca, where Port Angeles on the Olympic Peninsula shows counterclockwise turning while Victoria on Vancouver Island has an oppositely directed hodograph. The figure-eight-shaped hodograph at Olympia is interesting because Olympia is situated at the boundary between two regional sea breeze circulations; it is influenced by the Chehalis Gap to the south and Puget Sound to the north.

5. Summary The mid-latitude west coast marine climate of the Puget Sound region is typified in summer by a pattern of high pressure and in winter by a sequence of storms that originate over the ocean to the west. Local variations in climatic indicators such as precipitation and wind are substantially influ enced by the region's topography. The maximum precipitation occurs in early winter which results in a bimodal distribution of runoff into Puget Sound: there is a winter maximum associated with increased rainfall and a late spring maximum associated with snow melt. The proximity to the Pacific Ocean and the presence of Puget Sound has a moderating influence on extreme temperatures in both summer and winter. Over the waters of Puget Sound the winds near the surface flow from high to low sea-level pressure as imposed by the large- scale or regional weather pattern. Several local wind phenomena are important, the most notable being the formation of an orographically induced, mesoscale low-pressure region in the lee of the Olympic Mountains during strong onshore winds associated with major coastal storms. Such an event produced winds in excess of 50 m s-l in a localized area of Puget Sound at the time of the destruction of the Hood Canal Bridge.

57 .•.•.•..TTl .... '...... 1020 ~ .... ~.. ~.. ." ' .... 1019 ••••

-..c E -CL 2.0

-..c E 1017 1.0 CL

0.3 6.3 12.3 18.3 TIME (pst)

Figure 30. Average sea-level pressures at each hour of the day for July 1950 at Tatoosh Island (TTl), Port Angeles (PAE), Everett (EVE), Bellingham (BlI) (upper four curves); and sea-level pressure differences between Port Angeles and Bellingham, Port Angeles and Everett, and Tatoosh Island and Port Angeles (Staley, 1957).

58 Lynott, R.E. and D.P. Cramer (1966): Detailed analysis of the 1962 Columbus Day windstorm in Oregon and Washington. Monthly Weather Review, 94:105-117. Mass, C. (1981): Topographically forced convergence in western Washington state. Monthly Weather Review, 109:1335-1347. Mass, C. (1982): The topographically forced diurnal circulations of western Washington state and their influence on precipitation. Monthly Weather Review, 110:170-183. Maunder, W.J. (1968): Synoptic weather patterns in the Pacific Northwest. Northwest Science, 42:80-88. Mullen, S.L. (1979): An investigation of small synoptic-scale cyclones in polar air streams. Monthly Weather Review, 107:1636-1647. Myers, R.A. (1966): Lee troughing west of Vancouver Island. CIR-4410, TEC-608, Department of Transport-Meteorological Branch, 5 pp. National Climatic Center (1980): Local Climatological Data, Annual Summary, Seattle-Tacoma Airport. National Climatic Center, Asheville, N.C., 28801, 4 pp. Overland, J.E., M.H. Hitchman and Y.J. Han (1979): A Regional Surface Wind Model for Mountainous Coastal Areas. NOAA Technical Report, ERL-407 PMEL-32, Environmental Research Laboratories, National Oceanic and Atmospheric Administration, Boulder, Colorado, 34 pp. Overland, J.E. (1981): Forecasting the Pacific Northwest winds. Castoff, April 1981, 10-13. Overland, J.E. and B.A. Walter (1981): Gap winds in the Strait of Juan de Fuca. Monthly Weather Review, 109:2221-2233. Parsons, D.B. and P.V. Hobbs (1983): The mesoscale and microscale structure and organization of clouds and precipitation in midlatitude cyclones. VIII: Some effects of orography on rainbands. Submitted to Journal of the Atmospheric Sciences. Phillips, E.L. (1968): Washington climate for these counties, King, Kitsap, Mason, Pierce. Cooperative Extension Service, Washington State University, Pullman, Washington, 66 pp. Puget Sound Air Pollution Control Agency (1972-1980): Air Quality Data Summary for Counties of King, Kitsap, Pierce, Snohomish. Puget Sound Air Pollution Control Agency, 410 W. Harrison St., Seattle, Washington 98119. Reed, R.J. (1979): Cyclogenesis in polar airstreams. Monthly Weather Review, 107:38-52. Reed, R.J. (1980): Destructive winds caused by an orographically induced mesoscale cyclone. Bulletin of the American Meteorological Society, 61: 1346-1355. Reed, R.J. (1981): A case study of a bora-like windstorm in western Washing ton. Monthly Weather Review, 109:2383-2393. Reed, T.R. (1931): Gap winds of the Strait of Juan de Fuca. Monthly Weather Review, 59:373-376.

61 Reed, T.R. (1932): Weather types of the northeast Pacific Ocean as related to the weather of the north Pacific coast. Monthly Weather Review, 60: 246-252. -- Riley, J.J., H.T. Liu, and E.W. Geller (1976): A numerical and experimental study of stably stratified flow around complex terrain. u.s. EPA Environ mental Monitorin~ Series Report No. EPA-600/4-76-021, Research Triangle Park, North Caro ina, 30 pp. Schoenberg, S.A. (1983): Regional wind patterns of the inland waters of western Washington and souther British Columbia. NOAA Technical Memorandum, Environmental Research Laboratories, National Oceanic and Atmospheric Administration, Boulder, Colorado, (in press). Shore Protection Manual (1973): Vol. 1, U.S. Army Coastal Engineering Research Center, U.S. Government Printing Office, 496 pp. Skjelbreia, N. (1981): Floating breakwater prototype test program, Department of the Army, Seattle District, Corps of Engineers, (unpublished manuscript). . Smith, R.B. (1980): Linear theory of stratified flow past an isolated moun tain. Tellus, 32:348-364. Smith, R.B. (1981): An alternative explanation for the destruction of the Hood Canal Bridge. Bulletin of the American Meteorological Society, 62: 1319-1320. Staley, D.O. (1957): The low-level sea breeze of northwest Washington. Journal of Meteorology, 14:458-470. Walter, B.A. and J.E. Overland (1982): Response of stratified flow in the lee of the Olympic Mountains. Monthly Weather Review, 110: 1458-1473. Williams, R., H. Pearson, and J. Wilson (1982): Streamflow statistics and drainage-basin characteristics for the Puget Sound Region, Washington. Technical Reeort, U.S. Geological Survey, Water Resources Division, Tacoma, Washlngton, in press.