April 1969 351
UDC 651.513:551.515.7:551.677.37(794)"1969.1" THEWEATHER AND CIRCULATION OF JANUARY 1969 Continued Strong High-Latitude Blocking and Flood-Producing Rains in California
A. JAMES WAGNER
Extended Forecast Division Weather Bureau, ESSA ,Suitland, Md.
1. MEAN CIRCULATION The strongest blockingNorthernthe in Hemisphere was over Greenland where 700-mb heights averaged 170m Blocking, which had become strongin the Western abovenormal for themonth (fig. 2). Slightlyweaker Hemisphereduring December (Green, 1969), increased blocking was locatedbetween Spitzbergen and Novaya further during January 1969. The Aleutianridge con- Zemlya. The magnitude of thisextensive high-latitude tinued to build and developed asmall High center (see blocking shows in the zonal profile of sea-level pressure themonthly mean 700-mb map (fig. 1)) withheights as for January 1969 comparedwith theJanuary normal muchas 150 mabove normal (fig. 2). Anomalous flow(fig. 3). Sea-level pressureaveraged more than 8 mb from an unusually cold Canadian Arcticsource led to abovenormal north of 60" N. in the westernportion of frequent intensecyclogenesis just off the Paciiic Northwest the hemisphere. coast, reflected in a sharptrough with heights 110 m Cyclonic activity was stronger than normal in low and below normal. Flow froma separate center of cyclonic middlelatitudes from the eastern Atlantic through the activity north of Hawaii contributed to strong confluence Mediterranean, and over eastern Asia where surface Lows inthe Californiaarea. This helpedproduce record- cross the cold landmassinfrequently during midwinter. breaking heavy rains and disastrous floods in some areas The principal 700-mb monthly mean Low center which of the State. had been near the Taymyr Peninsula during December
FIGURE1.-Mean 700-mb contours (decameters) for January 1969.
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1035
1030
1025 - m -i YI IO20 3 v) Y), (I 0 1015
1010
IO05 90 75 70 65 60 55 50 45 40 35 30 25 20 LATITUDE ( DEGREES )
FIGURE3.-Mean sea level pressure profile for the western half of theNorthern Hemispherebetween 20' N.and the Pole.Solid line shows observed for January 1969, and dashed line indicates the January normal. FIGURE2.-Departure from normal of mean 700-mb height (deca- meters) for January 1969.
waterrelative to normal was also locatedabout 10' (see fig. 1 in Green, 1969) shifted to the Sea of Okhotsk farther north in 1962 (compare fig. 2 of Namias, 1963, (fig. 1) asheights fell rapidly over thenorthwestern with fig. 5A). Pacific and rose over the Arctic Basin. The watertemperatures cooled considerably relative The unusual circulation pattern during January 1969 to normal during January (fig. 5B) in thearea of cyclogen- around most of the Northern Hemisphere is demonstrated esis north of Hawaii, but remained a few degrees above by the positions of the various branches of the mean jet normal over most of the area from east of Hawaii to the streams (fig. 4). The westerlies were split intotwo branches California coast as tropical air was advected northeast- over both oceans; the northern branch was stronger inthe ward in the strong southwesterly flow at low latitudes Pacific, andthe southern branch was stronger inthe (figs. 1 and 2). The abnormallywarm water may have Atlantic. Over Asia and North America the jet stream increased the moisture content of these air m'asses above was south of its normal position. The strongest anomalies what it would have been otherwise. of wind speed were in thePacific where the blocking High, Water temperatures were also as much as 6'F above near the normal position of the jet south of the Aleutians normal in the western Pacific east of Japan (figs. 5A, B). (figs. 1, 4), reduced the mean 700-mb wind speed to 12 This additionalenhancement of the continent-ocean m/sec below normal, and the jet east of Hawaii produced temperaturecontrast may have further stimulated the a mean wind speed 12 m/sec above normal. intense cyclogenesis that occurred just to thenorth of The intensification of the deep and unusual Low north that area.However, as Namias (1969) pointsout, the of Hawaii, which was of crucial importance for the dis- wintertime,variability of the atmosphere .is smaller near astrous California rains, may be related to the preexistent the Asian coast than over thecentral Pacific. Hishy- distribution of sea-surface temperature in that partof the pothesis is that the climatological temperature contrast Pacific. During December, ocean temperatures north of between continent and ocean is so large that anomalies of Hawaii were more than 4°F above normal (fig. 5A). The water temperature near the coast change the magnitude normal seasonal southwardmovement of the westerlies of the thermal forcing field relatively little in that area. was aided this year by the blocking ridge south of the The January 1969, 700-mb height was only 70 m below Aleutians. The usually warm water and enhanced surface normal over Sakhalin (fig. 2) compared to 150 m above thermal gradient to the north of Hawaii may have stimu- normal south of the Aleutians and 90 m below normal lated abnormally strong cyclogenesis by providing greater north of Hawaii. than normal sensible and latent heat to the lower atmos- 2. MONTHLYWEATHER phere and impressing a low-level baroclinic fieldon air masses in the area. The unusualcirculation pattern over the western A physically similar situation that occurred somewhat portion of the hemisphereduring January 1969 was farthernorth was discussed in more detail by Namias related to strong contrast of temperature in the United (1963). In that case the center of negative height anomaly States. Confluence between Arctic air from Canada and was locatednear 40' N. (compare fig. SAof Namias, Alaska and subtropical air from the eastern Pacific led to 1963, with figs. 1 and 2) instead of 30' N. The warmest a mild GreatBasin and frigid Pacific -Northwestand
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FIGURE5.-Departure from normal of average sea-surface tempera- ture (OF) in the Pacific Oceanfor (A) December1968 and (B) FIGURE4.-Mean 700-mb geostrophicwind speed (meters per January 1969.Below normalareas areshaded, and areas more second)for January 1969. Solid arrows show axes of maximum than 2OF abcive normal have hatched lines (from Renner, 1968 wind speedduring January 1969, anddashed arrowsindicate and 1969, and from Japan Meteorological Agency, 1968 and 1969). normal January positions.
northern Rockies (fig. 6). Temperatures were more than 8°F above normal at Winslow, Ariz., and Ely, Nev., the second and third warmest January of record, respectively. In contrast, the monthly mean temperature (-2.8OF) in Great Falls, Mont., was nearly 25OF below normal, and Billings, Mont., had its third coldest January in 35 yr of airport recordsand the coldestDecember-January in 75 yr. Temperatures averaged more than 4OF below normal over the Northern Plains, the Mississippi River Valley, and parts of the Southeast. Mildness in northern New England was due to easterlyanomalous maritime flow from the Greenland blocking High (fig. 2). The rest of the Nation eastof the Mississippi River had temperatures near or slightly below normal (fig. 6). FIGURE6.-Departure from normal of average surface temperature Juneau, Alaska, which was under the almost continu- (OF) for January 1969 (from Environmental Data Service, 1969). ous influence of Arctic air, reported its coldest January of record,more than18°F below normal,and tied the recordfor dryness since normal Pacific moisture failed Storms frequently formed to the lee of the Rockies and to reach the coast. Other stations along the Alaskan coast followed paths towards the Great Lakes, leading to fairly also reported extreme cold and dryness during January. extensive areas of heavyprecipitation in the northern The most newsworthy weather items during January Mississippi Valley and parts of the Midwest. Much of this 1969 were the heavy rains andfloods in southernCalifornia. precipitation was inthe form of freezing rain.Several The abnormallystrong southwest flow associated with cities from central Nebraska to northern Indiana reported an unusual subtropical branch of the jet stream brought glazing conditions on 7 to 11 days. heavy precipitation to California and much of the Nation Many stations from the west coast to the Great Lakes west of the Divide (figs. 2, 4, 7). Extensiveareas had reported the wettest or snowiest January of record, and more than twice the normal January precipitation,and dozens more had near records. Some of the highlights from . parts of southern California received more thanfour these are shown in table 1. timestheir January normal (fig. 7).No surface Highs Many localities in the Far West,particularly in and entered the West from the Pacific along the normal near the Sierras,reported the heaviest seasonal snow primary anticyclone track through Oregon. accumulations through January 31 in history, well over
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RCENTAGE OF NORMALPRECIPITATION TABLE1.-Selected record or near-record total precipitation and Jonuwv l96P snowfall during January 1969
Station Quantity R0lUUkS (inches)
Los Angeles, Calif.: Civic Center ______14.94 Wettest January of record Airport ______- - ______9.00 do. Fresno, Calif______8.56 Wettest January in 91-yr record Blue Canyon, Cal if-...- 32.41 Wettest January of record Bishop, Cali______8.93 Wettest month of record -23.0. Snowiest January of record Long Beach,Calif ______11.24 Wettest Janukry of recod (since 1942) Sacramento, Calif______a 90 Wettest January in 50 yr and 0th wettest of record Eanta Maria, Calif ______7.09 Wettest January in 62 yr and6th wetbst of remrd Medford, Oreg______13.7 Third snowiest month ofrecord and 12 days with measurable snowset new record
Salem, Oreg.. ...___ ~ ____ 21.9 Third snowiest Januaryof record FIGURE7.-Percentage of normal precipitation forJanuary 1969 Walla Walla, Wash______4.17 Third wettest January since 1873 (from Environmental Data Service, 1969). 31.3 Snowiest January since 1846 Milford, Utah __.______1.63 Wettast January in 63 yr Boise, Idaho.. ._.____._.3.50 Wettest January since 1909 Helena, Mont ______2.78 Second wettest January since 1884 100 in. in some of the passes. Seattle-Tacoma Amport also 35.6 Snowiest Januaryof record Missoula, Mont__..__.___ 2.94 Tied for second wettest January of record reported a record seasonal snowfall total of 68 in. and a 27.5 Second snowiest January of record record total of 20 consecutive days with continuous snow Havre, Mont ______.___26.2 Snowiest January of reoord Kalispell, Mont ___.__.__34.2 Second snowiest January of record cover of an inch or more. Stampede Pass, Wash., with 171 Huron, S. Dak ______.___13.1 do. in. of snow on the ground by January31, reported measur- St. Cloud, Minn ..______2. 52 Second wettest January since 1897 Duluth, Minn ______46.8 Snowiest month of record able precipitation on every day of the month, nearly all of it falling as snow. Another measure of the storminess of this month is the number ?f stationsthat reported unusual amounts of cloudiness or low amounts of sunshine. Olympia, Wash., reported every day as cloudy and bad a monthly average sunrise-to-sunset sky cover of 9.7 tenths. Eugene, Qreg., 3. VARIABILITY WITHINTHE MONTH reported no clear days,and Spokane, Wash., only one. Fresno, Calif., had the least sunshine for any month since The circulation over North America underwenta
1900. ir considerable change aboutthe middle of January, so Although Albuquerque, N. Mex., reported only .08-in. the weather of thefirst 2 weeks maybe discussed in precipitation, which was 20 percent of the normal, the connection withthe mean 700-mb heights for the first number of cloudy days was twice normal, indicating that half of the month. With the aid of an extremely useful the “rainshadow effect” was onlyable to dryout the technique developed by Booth and Taylor (1968), it is lower layers of the atmosphere, where most of the pre- possible to show the meanbrightness of the Northern cipitable water is found. Hemisphere as measured bythe ESSA-7 satellitefor Goodland, Kans., reported 14 days of fog, a new record almost the same period (fig. 8). Of particular interest is for anymonth. Omaha, Nebr., had only 22 percent of the bright area associated with the active trough northof possible sunshine, the least for any January since 1911. Hawaii where several stations reported heavy rains the Topeka, Kans., and Huron, S. Dak., set new records for first few days of January. The snow cover and cloudiness the most cloudy days in January with22 each. over the Northwest and Northern Plains stands out as Cold air aloft, sweeping inland from the Pacific with one of the brightest areas of the hemisphere. The southern vigorous short wave troughs, contributed to some unusual and eastern United States, which were cold and relatively convectiveactivity in the West also. Astoria, Oreg., dry (figs. 9A, B and 10A, B), show up as rather darkareas. reported hail on 10 days of the month, and thunderstorms Note how the mean brightness increases just off the east withhail were observed twice at Salt Lake City, with coast, near the prevailing trough line (fig. 8) and where January 1969 the second January to have any reports of convective activity is vigorous when unusually cold air hail since records have been kept at the airport. masses move from the continent during winter. With all the cyclonic activityconcentrated in the The first 2 weeks of the monthwere relatively mild over West andthe central part of theNation, there was a the Far West and cold from the Divide to the Atlantic dearth of snow and precipitation in parts of the South coast,asanticyclonic conditions prevailed over the and East (fig. 7). Boston, Mass., and Washington, D.C., Rockies and the blocking High over Greenland trapped
I had less than an inch of snowfall for themonth. Prov- a.closed Low near the Gulf of St. Lamence. This brought idence, R.I., reported the third least snow, and Hartford, Arctic air into the East in strength (figs. 9A and lo&. Conn., the third least precipitationfor any January of Heavyprecipitation, except fora small area nearthe record. PortArthur, Tex., reported the second driest, Gulf Coast, was confined to the Pacific Northwest during and Jackson, Miss., the driest January of record. the first week of themonth. During the second week
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FIGURE &--Mean 700-mb contours (decameters) for Jan. 1-15, 1969,superimposed upon mean brightness composite photograph of daily observations from theESSA-7 satellite for Dec. 30, 1968-Jan. 13, 1969.
(figs. 9B and lOB), rain moved southward into northern also established at several stationsin the easternand California as the flow began to change from anticyclonic southern United Statesduring the.firstweek of the month. to cyclonic. A vigorous burst of warmth crossed thesouthern During the first few days of the month, extremely low Rockies on the 7th and 8kh of January in an extremely temperatureswere observed inthe interior of Alaska. strong westerly flow. A maximum temperature of 64OF New daily minimum recordswere established at Fairbanks on the 7th was the warmest ever observed in January in the first 5 days of January, with the coldest being -61OF 32 yr of record at Wendover,Utah. The next dayin on the 2d. Tanana reported minima below -60°F on the Texas, readings of 87°F at Wichita Falls, 88°F at Dallas, first 3 days, with the 2d having a mean of -6loF and a and 90°F atSan Angelo equaled the record highs for minimum of -63'3''. New daily minimum records were January, and a temperature of 82OF at Lubbock estab-
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&!"---P,fDEPARIURE.. V.% OF AVERAGE. TEMPERATURE. .- ._.- FROM NORMA.! ('F)
FIGURE9.-(A) departure from normal of average surface tempera- FIGURE10.-(A) and (B) same as figure 9, for week of Jan. 6-12, ture (OF) and (B) tot.al precipitation (inches) for week of Dec. 1969 (from Environmental Data Service, 1969). 30, 1968-Jan. 5, 1969 (from Environmental Data Service, 1969).
fished a new mark for January warmth. Damaging winds were observed at several places in eastern Colorado, with
* peak gusts over 100 mi hr". at Boulder. Large changes in the circulation occurred between the first and second halves of January. Half-monthly mean 700-mb heights fell by 250 rn in the western Bering Sea and forced the Aleutian ridge eastward. Heights increased 190 m in theGulf of Alaska. The Hawaiian trough moved eastward and joined the west coast trough to produce the record-breaking rainsand floods in southernCalifornia (figs. 11, 12). The center of blocking moved southward from Green- land to eastern Canada, and 700-mb heights rose 210 m over Maine.Temperatures moderated rapidly over the easternUnited States (figs. 13A, 14A), but Arcticair persisted in the Northwest and NorthernPlains. The eastward progression of the Hawaiian troughshows clearly on the ESSA-7 mean brightness photograph with the brightest area in the region of strong southwesterly flow(fig. 12). Note the unusual darkness of the eastern FIGURE11.-Change in half-monthlymean 700-mb height (deca- Gulf of Alaska where abnormallystrong transport of meters) between Jan. 1-15 and Jan. 16-31, 1969.
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FIGURE12.-Same as figure 8; contours for Jan. 16-31, 1969, and photograph for Jan. 14-28, 1969.
dry Arctic air in a northerly flow with only slight cyclonic The heaviest rains in California fell during the fourth curvaturekept this usually cloudy region relatively week, with more than 12 in. in some coastal areas (fig. cloud free. 14B). Bishop, Calif., establishedJanuary a 24-hr maximum The snowy andstormy Northern Plains showed up snowfall record of 18.0 in. and Presno, Calif., a January even brighter during the second half of the month, and 24-hr maximumrainfall record of 2.59 in.on the 24th moderately increased brightness over the South and East and 25th of the month. were related to increased precipitation and cloudiness in Several recor\ds for persistent cold were established in ' those areas (figs. 13B, 14B). theNorthwest. ' Seattlereported 10 consecutive days
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-- .. . DEPARTURE OF AVERAGETEMPERATURE FROM NORMA.! (OF) -k
FIGURE13.-(A) and (B) same as figure 9, forweek of Jan. 13-19, FIGURE14.-(A) and (B) same as figure 9, for week of Jan. 20-26. 1969 (from EnvironmentalData 1969).Service, 1969.
during which the temperature failed to rise above freezing REFERENCES and Sheridan, Wyo., had 16 consecutive subfreezing days. Booth, A. L., and Taylor, V. R., “Meso-Scale Archive and Products The latter station also reported 19 days in all throughout of Digitized Video Data from ESSA Satellites,’) Technical Memo- the month in which the minimum temperature was below randum No.NESCTM 9, NationalEnvironmental Satellite zero, compared to a normal of six. Numerous daily low Center, ESSA, Washington, D.C., ,Oct. 1968, 25 pp. EnvironmentalData Service,ESSA, WeeklyWeather and Crop temperature records were also established during the last Bulletin, Vol. 56, Nos. 1-6, Jan. 6, 13, 20, 27 and Feb. 3 and 10, week of January at Havre, Mont., andWilliston, N. Dak. 1969, pp. 1-8. After the Hawaiiantrough moved eastwardtoward Green, R. A., “The Weather and Circulation of December 1968- California, the southward advection of relatively cool air Strong Blocking Over the Western Hemisphere and Cold in the from the .north .and daytime cloudiness. associated yith UnitedStates,” MonthlyWeather Review, Vol.97, No. 3, Mar. 1969, pp. ‘281-286. lingering instability in the still cyclonic flow combined to Japan MeteorologicalAgency, The TenDay Report, Tokyo, I968 setmany daily low records for maximum,minimum, and 1969, (series of 10-day mean sea-surface temperature analyses and mean temperature in Hawaii.A new all-time low available three times each month). temperature record of 48OF was established at Kahului Namias, J., “Large-Scale Air-Sea Interactions Over theNorth on the 20th, and new January minima were set at Lihue Pacificfrom Summer 1962 throughthe Subsequent Winter,” Journal of GeophysicalResearch, Vol.68, No. 22, Nov. 1963, (50°F) on the 22d and at Milo (54°F) on the 23d. pp. 6171-6186. An unusualJanuary tropicalstorm, Phyllis, moved Namias, J., “Seasonal Interaction Between theNorth Pacific throughthe western Pacific at very low latitudesand Ocean and the Atmosphere During the 1960’~~”Monthly Weather reachedtyphoon intensity for a while. January records Review, Vol. 97, No. 3, Mar. 1969, pp. 173-192. were set for fastest 1-min wind speed (55 mi hr-l), 24-hr Renner, J. A., “Sea-Surface TemperatureCharts, Eastern Pacific Ocean,” California Fisheries Market News Monthlg YummaTy: II. precipitation (3.66 in.),and lowest sea-level pressure FishingInformation, Fishery-OceanographyCenter, Bureau of (29.34 in.) at Kwajalein Island as it passed 25 mi to the Commercial Fisheries, La Jolla, Calif., Dec. I968 and Jan. 1969 north. 8 pp. (see p. 4). US. GOVERNMENT PRINTING OFFICE: 1969 “335-328
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