702 WEATHER AND FORECASTING VOLUME 13

The Sundowner Winds of Santa Barbara, California

WARREN BLIER Department of Atmospheric Sciences, University of California, Los Angeles, Los Angeles, California (Manuscript received 10 September 1996, in ®nal form 24 February 1998)

ABSTRACT Signi®cant downslope wind and warming events periodically occur along a short segment of the southern California coast in the vicinity of Santa Barbara. This region is characterized by a unique mesoscale topography: over a length of about 100 km the coastline is oriented approximately west±east, with the adjoining narrow coastal plain bounded by a steeply rising (to elevations greater than 1200 m) and coast-parallel mountain range. Called Sundowner winds because they often begin in the late afternoon or early evening, their onset is typically associated with a rapid rise in temperature and decrease in relative humidity. In the most extreme Sundowner wind events, wind speeds can be of gale force or higher, and temperatures over the coastal plain, and even at the coast itself, can rise signi®cantly above 37.8ЊC (100ЊF). In addition to causing a dramatic change from the more typical marine-in¯uenced local weather conditions, Sundowner wind episodes have resulted in signi®cant property and agricultural damage, as well as extreme ®re danger. They have, in fact, been associated with many of the most destructive con¯agrations that have occurred in the Santa Barbara region. In the present study, three different Sundowner wind episodes are examined. These include midsummer and midautumn events primarily manifested by extremely warm temperatures, and a winter season event notable for its damaging winds. The associated meteorological conditions are examined, and possible physical mechanisms responsible for these episodes are discussed. In at least two of the three cases considered here, mountain wave development appears to have played a signi®cant role.

1. Introduction number of large midlatitude mountain ranges (e.g., the Numerous observational and modeling studies have Front Range of the Rocky Mountains, the Sierra Nevada shown that mountain barriers can exert a signi®cant in- of California), this is not necessarily the case when these ¯uence on atmospheric ¯ows. Various modalities in this phenomena are associated with orographic features of regard exist; these include drainage ¯ows, blocking or much smaller length scale. Effects can nonetheless be damming phenomena, ¯ow funneling, induction of cy- dramatic and can have signi®cant impact on the local clonic circulations (e.g., Denver cyclone, Catalina environment. The induced change from more typical eddy), and mountain wave development and associated meteorological conditions can be particularly striking in downslope wind events. The last of these appears to be those situations where the mountain range adjoins a of greatest relevance to the Sundowner events discussed coastline; conceptual complexity also increases as in- in the present paper. ¯uences of the large-scale land±ocean thermal contrast Mountain waves are simply gravity waves forced by and variation in boundary layer structure need to be mountains. As noted by Durran (1990) and others, large- considered, as well as the shape of the coastline itself. amplitude mountain waves can be associated with strong Perhaps the most dramatic examples of coastal down- surface winds that blow down the lee slope of the moun- slope wind events within the contiguous United States tain (range)Ðwith wind gusts in excess of 50 m sϪ1 (97 are those that periodically occur along a short segment kt) in extreme events. Signi®cant warming can also be of the southern California coast in the vicinity of Santa produced on the lee side of the mountains by the down- Barbara. The term ``Sundowner'' has long been used to slope winds. refer to these downslope winds because of their typical Although mountain wave development and associated onset in the late afternoon or early evening. Associated downslope wind events have been well studied for a with a rapid rise in temperature and decrease in relative humidity, the most intense events of this sort can bring extremely warm temperatures and/or damaging winds. The region susceptible to these Sundowner winds is Corresponding author address: Dr. Warren Blier, National Weather Service, 21 Grace Hopper Ave., Bldg. 712, Monterey, CA 93943- characterized by a mesoscale topography unique within 5505. the conterminous United States (Fig. 1): a coastline that E-mail: [email protected] is oriented east±west for a distance of approximately

᭧ 1998 American Meteorological Society

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FIG. 1. (a) Map of southern portion of California, with locations of key stations VBG (Vandenberg Air Force Base), SMX (Santa Maria), and SBA (Santa Barbara) indicated. (b) Expanded view of mesoscale region of interest with key locations and geographical features identi®ed. Contours in (b) indicate surface elevation: dashed line ϭ 500 m, solid line ϭ 1000 m, and hatched regions Ͼ1500 m. Lake Cachuma indicated by stippling.

100 km, with the adjoining narrow coastal plain bound- The only incident of the simoom1 on this coast, mentioned ed by the coast-parallel and steeply sloped Santa Ynez either in its history or traditions, was that occurring at Mountains (peak elevation approximately 1300 m). Santa Barbara, on Friday, the 17th of June 1859. The [Somewhat similar warm episodes that have occurred temperature during the morning was between 75Њ and along limited segments of the coast of southern Oregon 80Њ, and gradually and regularly increased until about and northern California have been examined by Mass one o'clock p.m., when a blast of hot air from the north- (1987).] west swept suddenly over the town and struck the in- In the most severe Sundowner wind events, wind habitants with terror. It was quickly followed by others. speeds can be of gale force or higher and surface air At two o'clock the thermometer exposed to the air rose temperatures on the coastal plain, and even at the coast to 133ЊF, and continued at or near that point for nearly itself, can well exceed 100ЊF (37.8ЊC). The associated three hours, whilst the burning wind raised dense clouds ®re danger can become extreme under the combination of impalpable dust. No human being could withstand the of high temperatures, low relative humidity, and strong heat. All betook themselves to their dwellings and care- and gusty windsÐcircumstances dramatically different fully closed every door and window. The thick adobe than the more typical marine-in¯uenced local weather walls would have required days to have become warmed, conditions. Many of the most destructive con¯agrations and were consequently an admirable protection. Calves, that have occurred in the Santa Barbara region, includ- rabbits, birds, etc., were killed; trees were blighted; fruit ing the Painted Cave ®re of June 1990, which was was blasted and fell to the ground, burned only on one among the more devastating ®res in California history side; and gardens were ruined. At ®ve o'clock the ther- (losses in public and private buildings totaled almost mometer fell to 122Њ, and at seven it stood at 77Њ.A $250 million), have occurred during one of these wind ®sherman, in the channel in an open boat, came back episodes. with his arms badly blistered. During the Painted Cave ®re Sundowner event, the of®cial Federal Aviation Administration (FAA) observ- As no similarly high temperatures have been achieved ing station at Santa Barbara airport reported a maximum during the subsequent 100ϩ year period of standardized temperature of 109ЊF (42.7ЊC), remarkable for a location weather observation in Santa Barbara, it is uncertain on the coastal plain within 2 km of the ocean itself whether these temperature reports are accurate. None- [where the sea surface temperature was approximately 65ЊF (18.3ЊC)]. As noted by Ryan and Burch (1992) and Ryan (1994), however, even this wind event pales in comparison to the 17 June 1859 Ssundowner. A rather 1 A ``poison wind,'' de®ned by the Glossary of Meteorology (Huschke 1959) as ``a strong, dry, dust-laden desert wind which blows dramatic and colorful description of this event is pro- in the Sahara, Palestine, Syria and the desert of Arabia'' with a tem- vided by the following passage taken from the Coast perature that ``may exceed 130ЊF'' and a humidity that ``may fall Pilot of California (Davidson 1869). below 10 percent.''

Unauthenticated | Downloaded 09/27/21 04:21 AM UTC 704 WEATHER AND FORECASTING VOLUME 13 theless, it is quite evident that remarkably high tem- vicinity of Santa Barbara were generally available to us peratures are sometimes observed along a short stretch from only the FAA site at Santa Barbara airport (SBA).2 of the California coast in the region of Santa Barbara. And, as noted by Ryan (1996), this can be among the Thus far, however, little in the way of synoptic or last locations on the coastal strip to manifest Sundowner climatological analysis of these events has yet been pub- conditions. Observations from SBA alone may fail to lished. This paper is thus among the ®rst to examine in indicate a Sundowner event clearly evident elsewhere some detail the meteorological conditions associated in the city. It also is not clear that one would necessarily with several signi®cant Sundowner wind events. want to classify every incident of downslope ¯ow and associated warming anywhere on the mountain slope as a Sundowner event. Rather, it would seem more appro- 2. Methodology priate, especially in consideration of the long-standing A rigorous de®nition of a Sundowner wind event has local popular use of the term, to con®ne its application not yet been provided in the literature. Finke (1990) to those cases that have a signi®cant impact on the me- simply characterizes the Sundowner as the sudden onset teorological conditions (i.e., wind and/or temperature) of strong desiccating winds from the north to northeast on the populated coastal plain. (Conditions on the moun- accompanied by a rapid rise in temperature and decrease tain slope itself would, of course, nonetheless be of in humidity. Ryan and Burch (1992) and Ryan (1996) critical importance to the ®re weather situation.) classify warming events in the vicinity of Santa Barbara In the present study we investigated the synoptic- into four categories, the ®rst being a non-Sundowner scale meteorological conditions associated with three warm event and the other three representing different Sundowner events that did produce signi®cant wind and/ intensities of Sundowner events. In their classi®cation or warming at the of®cial FAA site. In addition to con- system, Sundowner events are distinguished from other sidering the degree of departure of the maximum tem- warm episodes by the strength and direction of the sur- perature from the normal diurnal pro®le [following face winds and by the time of day of the maximum Ryan and Burch (1992) and Ryan (1996)], we also ex- temperature at Santa Barbara: in the Sundowner case, amined the hourly positive temperature difference be- surface winds tend offshore even at the coast, and the tween Santa Barbara and Santa Maria (on the coastal maximum temperature occurs outside the normal diurnal plain to the northwest of the Santa Ynez Mountains). temperature pro®le. Both stations are typically under the in¯uence of ther- Given the coastal location of Santa Barbara and the modynamically similar cool and moist maritime air, but climatologically cool sea surface temperatures of even during a Sundowner event the temperature at Santa Bar- the nearshore water (less than 20ЊC throughout the year), bara will increase.3 it is hard to envision the occurrence of much warmer In two of the three Sundowner events considered in than average temperatures except in the presence of re- the present paper, the most signi®cant manifestation in gional-scale offshore (and thus downslope) ¯ow, re- weather conditions observed at Santa Barbara was the gardless of the time of day the anomalously high tem- degree of warming that occurred, while the third event peratures are observed. In addition, local correspon- was accompanied by winds of destructive force. In the dence at and near the coast between the strength of the July 1992 case, the maximum temperature difference offshore-directed component of the wind and the mag- between SBA and Santa Maria (SMX) was 35ЊF nitude of the anomalous increase in temperature is less (19.4ЊC) at 0000 UTC 20 July (1700 PDT 19 July); the than robust. In some cases, weak onshore ¯ow is ob- high temperatures at SBA and SMX were 106ЊF served at Santa Barbara despite the presence of very (41.1ЊC) and 76ЊF (24.4ЊC), respectively. In the No- warm air temperatures, low relative humidity, and larg- vember 1992 episode, the maximum temperature dif- er-scale offshore-directed lower-tropospheric ¯ow. As ference was 23ЊF (12.8ЊC) at 0000 UTC 3 November shown in Blier and Ma (1997) in a high-resolution me- (1600 PST 2 November), while high temperatures were soscale modeling study of the 1995 New Year's Eve Sundowner wind event, this can result from a local rotor circulation downwind of the lee side of the mountain range. There have also been cases in which downslope 2 Ryan and Burch (1992) and Ryan (1996) did obtain some ob- winds, in association with anomalously high tempera- servations from additional nonstandard sites (e.g., those administered tures and low relative humidity, occur in the mountains by a ®re department or water district) in the Santa Barbara region, just above Santa Barbara, while typical maritime con- including some on the mountain slope and in passes through the mountain range. Such data, though potentially valuable, are not readi- ditions are evident in Santa Barbara adjacent to the ly or easily accessible and were not obtained in the present study. coast. 3 Infrequently, synoptic-scale east-northeasterly lower-tropospheric To identify the presence of a downslope wind event, ¯ow occurs in the region; this can result in offshore winds and warm- then, it might seem desirable to consider observations ing at both Santa Barbara and Santa Maria. Even under these con- ditions, however, greater warming would be expected at Santa Bar- from locations farther inland, at the base of the lee slope bara, given the closer proximity of the San Rafael Mountains and of the Santa Ynez Mountains, or on the mountain slope Sierra Madre, and the additional in¯uence of the Santa Ynez Moun- itself. Unfortunately, routine hourly observations in the tains.

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TABLE 1. Santa Barbara (SBA) and Santa Maria (SMX) observations from 1300 UTC 19 July 1992 to 0200 UTC 20 July 1992. Note: msg ϵ missing. SBA SMX

UTC (PDT) T(ЊF) Td (ЊF) SLP (mb) Wind (kt) T(ЊF) Td (ЊF) SLP (mb) Wind (kt) 1300 (0600) 63 60 1013.5 Calm 56 56 (msg) SW 4 1400 (0700) 67 61 1013.2 Calm 56 56 (msg) NNW 3 1500 (0800) 73 62 1014.6 Calm (msg) (msg) (msg) (msg) 1600 (0900) 79 62 1014.2 SE 8 (msg) (msg) (msg) N5 1700 (1000) 76 62 1014.2 SE 9 71 58 1017.3 WSW 4 1800 (1100) 76 62 1014.6 SSE 7 73 58 1017.3 NW 8 1900 (1200) 76 62 1014.2 SE 7 72 58 1017.1 WNW 10 2000 (1300) 80 62 1013.2 SSE 8 71 58 1016.8 NW 14 2100 (1400) 81 62 1012.5 S6 73 57 1016.6 WNW 13 2200 (1500) 89 64 1011.2 SW 6 71 57 1016.1 WNW 13 2300 (1600) 99 57 1010.5 S7 71 57 1015.7 WNW 11 0000 (1700) 106 47 1009.8 N10 71 57 1015.2 WNW 10 0100 (1800) 100 45 1009.8 W11 69 57 (msg) WNW 12 0200 (1900) 94 46 1010.5 WNW 12 65 57 (msg) WNW 14

98ЊF (36.7ЊC) at SBA and 84ЊF (28.9ЊC) at SMX. The temperature at Santa Maria was 71ЊF (21.7ЊC). In ad- third case is the New Year's Eve 1995 windstorm, where dition to the 35ЊF (19.4ЊC) temperature difference, the gusts of 44 kt (22.7 m sϪ1) were reported at SBA (though high temperature at SBA clearly occurred much later in higher values may well have occurred at times of miss- the day than average, consistent with the de®nition of ing reports); unof®cial reports and wind damage, how- Ryan and Burch (1992) and Ryan (1996). Hourly weath- ever, suggest that elsewhere in Santa Barbara wind er reports from both stations are presented in Table 1. speeds locally exceeded 70 kt (36.0 m sϪ1). During this These observations show that the rapid increase in tem- evening event, the temperature difference between Santa perature at SBA occurred during the 3-h period from Barbara and Santa Maria reached approximately 12ЊF 2100 to 0000 UTC, while little temperature change oc- (6.7ЊC) (missing reports from both sites precluded exact curred at SMX during this time period. Interestingly, determination of the maximum temperature difference). though, a north wind was evident at Santa Barbara only at 0000 UTC; at earlier times the wind remained south- 3. The 19 July 1992 Sundowner event erly-southwesterly and thus was blowing from the coast despite the temperature increase that was occurring At 0000 UTC 20 July 1992 (1700 PDT 19 July 1992), [suggestive of a low-level rotor circulation over the the temperature at Santa Barbara airport was 106ЊF nearshore waters to the lee of the Santa Ynez Mountains, (41.1ЊC), the high temperature for the day, while the as was found by Blier and Ma (1997) in a high-reso- lution numerical simulation of the 31 December 1995 Sundowner event, or some other local circulation in which strongly heated air quickly recirculated onshore]. Thus at the location of SBA, the Sundowner (offshore) wind itself was short lived and relatively weak, but the prior dramatic temperature increase provides evidence for the presence of the associated subsided air (though the absence of a commensurate decrease in the dewpoint suggests some remaining marine in¯uence). Thus just above the station and through the passes and along the mountain slopes, there may well have been signi®cantly stronger and more persistent offshore ¯ow. Such a con- trast in winds was noted in the extreme Sundowner event of 27 June 1990, associated with the Painted Cave ®re. Forest Service and Sheriff's Department personnel re- ported winds speeds up to 40±60 mph (17.9 m sϪ1 to 26.8 m sϪ1) in the Santa Ynez Mountains (Gomes et al. 1993), signi®cantly stronger than at SBA itself (though the ®re-induced circulation may have also contributed FIG. 2. Mesoscale plot for 0000 UTC 20 July 1992. Temperature to the strength of the wind). and dewpoint in ЊF, otherwise standard meteorological conventions apply. For land (marine) stations, parenthetical number below station The mesoscale data plot for 0000 UTC 20 July 1992 marker indicates elevation above sea level in m (SST in ЊF). (Fig. 2) shows the dramatic contrast in temperature that

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FIG. 3. NCEP 500-mb analysis for 0000 UTC 20 July 1992. FIG. 4. NCEP 850-mb analysis for 0000 UTC 20 July 1992. developed over a short distance in the vicinity of Point Barbara concurrent with the development of the eddy Conception. Cool temperatures and signi®cant ¯ow out (see Fig. 5 in Bosart 1983). The exact relationship be- of the northwest are evident from the buoy reports to tween these two phenomena (Sundowner winds and Cat- its west and north. Santa Maria on the coastal plain to alina eddies), however, remains to be determined. It is the north of Point Conception is under the in¯uence of conceivable, for example, that a Catalina eddy could this maritime air while signi®cantly warmer tempera- develop without the subsidence warming to the lee of tures are reported from stations in the hills and valleys the Santa Ynez Mountains reaching the surface at Santa more protected from the ocean winds. The warmest tem- Barbara; the approach of an upper-level trough from the perature, however, is at Santa Barbara on the narrow west and effects of the dramatic change in orientation coastal plain to the lee of the Santa Ynez Mountains. of the coastline in the vicinity of Point Conception on Also apparent is a strong mesoscale gradient in the sea the boundary layer ¯ow might also play a signi®cant level pressure, with lowest pressures in the vicinity of role in some cases of eddy development. Santa Barbara. An eddy circulation is evident from the At 0000 UTC 20 July, weak and generally westerly wind reports to the southeast of Santa Barbara; the buoy winds are evident at the 500-mb level (Fig. 3) over the temperature report of 73ЊF (22.8ЊC) with a west-south- region of south-central California, while the 850-mb westerly wind and a sea level pressure of 1010.4 mb ¯ow (Fig. 4) is more meridionalÐbetween an inverted indicates that some of the subsided air may be in®l- ridge offshore and an inverted trough over the inter- trating this circulation. A relatively common mesoscale mountain states and the desert Southwest. At Vanden- low-level cyclonic circulation in this region, referred to berg Air Force Base (VBG), near Santa Barbara, the as the Catalina eddy, has long been recognized. In fact, 500-mb wind is from the west-northwest at 25 kt (12.9 in a study of the 26±29 May 1968 Catalina eddy event, msϪ1), while at 850 mb the wind direction is more Bosart (1983) showed that the circulation of the incip- northwesterly and the wind speed slightly greater: 30 ient eddy initiated on the coast near Santa Barbara, and kt (15.4 m sϪ1). Thus the component of the wind per- that this developed in association with lee troughing pendicular to the Santa Ynez Mountains is greater at downwind of the coastal mountains. It was therefore 850 mb than at 500 mb. A more substantial temperature speculated that mountain wave activity, occurring in the gradient also appears at the 850-mb level than at 500 presence of synoptic-scale subsidence and with the gen- mb. While relatively uniform warm temperatures are eration of a stable layer near the crest of the local (Santa evident at the 500-mb level (Fig. 3), there is a signi®cant Ynez) mountains, may have aided the incipient eddy northwest-to-southeast temperature gradient at 850 mb formation. Data presented by Bosart are consistent with (Fig. 4). The 850-mb temperature increases from 20ЊC the occurrence of a Sundowner wind event in Santa at Oakland on the north-central coast of California to

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FIG. 5. NCEP surface analysis for 0000 UTC 20 July 1992. Temperature and dewpoint in ЊF, otherwise standard meteorological conventions apply. Report from Santa Barbara indicated by a box.

23ЊC at VBG, 26ЊC at San Diego, and 30ЊC at Tucson those reported in the hottest inland desert locations of in southern Arizona, while the 500-mb temperature at southern California. San Diego (Ϫ5ЊC) is only 1ЊC warmer than that at Oak- The VBG sounding from 0000 UTC 20 July 1992 land. (Fig. 6) shows the presence of a very strong low-level The National Centers for Environmental Prediction marine inversion. A cool, well-mixed layer of marine (NCEP, formerly known as the National Meteorological Center) surface analysis for 0000 UTC 20 July (Fig. 5) shows a signi®cant synoptic-scale pressure gradient from west-northwest to east-southeast in the vicinity of southern California. While Thermal in the low desert reports a sea level pressure of 1004.1 mb, the pressure at VBG is more than 10 mb higher at 1015.2 mb. Even over the relatively short distance between SBA and SMX, however, there is a difference in sea level pressure of 5.4 mb at 0000 UTC 20 July (Fig. 5 and Table 1). Note that the machine-analyzed contours fail to capture the mesoscale area of low pressure in the vicinity of SBA (reporting a pressure of 1009.8 mb). The contrast between the temperature at Santa Barbara (106ЊF) and at other coastal locations is strikingly apparent. In fact, the temperature at SBA is only a few degrees less than FIG. 6. VBG sounding for 0000 UTC 20 July 1992.

Unauthenticated | Downloaded 09/27/21 04:21 AM UTC 708 WEATHER AND FORECASTING VOLUME 13 air extends from approximately 1000 to 970 mb, with a temperature of approximately 14ЊC at the top of this layer. Between 970 and 950 mb, the temperature warms almost 13ЊC, reaching approximately 27ЊC at the top of the inversion. A thin isothermal layer is apparent from 950 to 920 mb, then the temperature decreases signif- icantly with height. This Sundowner event thus occurs in the apparent absence of a strongly stable layer at (or just above) the level of the ridgetop of the Santa Ynez Mountains, which at 1000±1300 m would be in the approximate pressure range of 880±910 mb. It is instructive to examine the level from which air on this sounding would have to subside dry adiabatically in order to achieve the temperature of 106ЊF (41.1ЊC) reported at SBA at 0000 UTC 20 July. This can be determined by simply following a dry adiabat on the FIG. 7. NCEP plot of temperatures (ЊF) reported by various south- thermodynamic diagram (Fig. 6) from the point speci- ern California stations at 2100 UTC 2 November 1992. ®ed by this temperature and the pressure level of mea- surement (which to a good approximation is simply the sea level pressure, 1009.8 mb, given that the station only a brief period of time. If so, then a mechanism elevation is only 3 m) to the point of intersection with capable of producing subsidence of air from well above the temperature pro®le. Following this procedure, a the mountaintop level, such as mountain wave activity, pressure level of 810 mb is found. This is well above would be suggested. the top of the Santa Ynez Mountains and, thus, would imply the presence of a dynamical mechanism capable 4. The 2 November 1992 Sundowner event of bringing air from well above the mountaintop level down to sea level on the lee side (e.g., mountain wave Another dramatic example of local warming in the activity). It is, however, not uncommon for the near- vicinity of Santa Barbara in association with downslope surface lapse rate to become superadiabatic (typically winds occurred on 2 November 1992. Temperatures (ЊF) by a few ЊC) on a hot summer day as a consequence of reported at various locations in the southern half of Cal- strong surface heating. Thus the foregoing calculation ifornia at 2100 UTC (1300 PST) are shown in Fig. 7. is repeated, but now assuming that the adiabatic ascent With a temperature of 96ЊF (35.6ЊC), SBA is signi®- only needs to warm the temperature to 38.1ЊC (100.6ЊF), cantly warmer than any other reporting station, includ- with diabatic processes producing the additional 3ЊC ing those in the interior desert regions. The contrast in (5.4ЊF) needed to reach the observed temperature. Under temperature is even more dramatic when SBA is com- these conditions the air would only have to subside from pared with other coastal locations in central and south- approximately the 860-mb level in order to account for ern California. The concurrent temperature at SMX (not the high temperature reported at SBA, or a level not far shown) was 81ЊF (27.2ЊF), which although quite warm above the ridgetop. It appears, then, that the high tem- is still 15ЊF (8.3ЊC) lower than at SBA. One hour later, perature observed at SBA could occur without subsi- at 2200 UTC, the temperature at SMX had decreased dence from a level signi®cantly above the top of the to 73ЊF (22.7ЊC) as the wind shifted to onshore, while mountains. winds remained offshore at SBA with a temperature of It is also conceivable that the very warm temperature 95ЊF (35.0ЊC). The high temperature at SBA on 2 No- could result simply from transport of hot surface air vember was 98ЊF (36.7ЊC), quite remarkable for a mid- over the Santa Ynez Mountains from the valley to its latitude coastal location in the month of November. north [as suggested by Ryan and Burch (1992)]. On 19 Table 2 shows the dramatic rise in temperature that July 1992, the maximum temperature at Lake Cachuma occurred at SBA between 2000 and 2100 UTC 2 No- was 98ЊF (36.7ЊC) at an elevation of 240 m. Simple vember. As in the previous case, however, this temper- adiabatic subsidence of this air to sea level would raise ature increase occurs in the absence of north winds at its temperature to 102ЊF (38.9ЊC). It is quite possible, the observation site itself; again SBA appears to be though, that as a result of sensible heat ¯ux from the within a local reverse circulation situated to the lee of surface, this air would cool at less than the dry-adiabatic the mountains. Despite a local wind direction indicating lapse rate as it ascends the windward slope of the moun- ¯ow from the nearby coast, the dewpoint temperature tains. Thus transport of this air over the mountains to has decreased signi®cantly, demonstrating the presence SBA could well account for the high temperature re- of much drier air; thus the air arriving at SBA from the ported. On the other hand, a location near SBA might south is likely subsided air originating over the moun- have experienced a higher temperature than SBA itself, tains to the north of the station, rather than air with a especially as northerly winds were reported at SBA for signi®cant overwater trajectory.

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TABLE 2. Santa Barbara (SBA) and Santa Maria (SMX) observations from 1300 UTC 2 November 1992 to 0200 UTC 3 November 1992. Note: msg ϵ missing. SBA SMX

UTC (PST) T(ЊF) Td (ЊF) SLP (mb) Wind (kt) T(ЊF) Td (ЊF) SLP (mb) Wind (kt) 1300 (0500) 52 48 1015.9 SSW 4 67 53 (msg) N10 1400 (0600) 52 48 1015.6 NNW 4 67 53 1019.8 N12 1500 (0700) 56 50 1015.9 NE 4 67 53 1019.8 NNE 13 1600 (0800) 67 54 1016.3 N3 71 53 1019.9 NNE 9 1700 (0900) (msg) (msg) (msg) (msg) 74 53 1020.1 NNW 14 1800 (1000) 83 54 1015.9 W9 76 53 1019.2 NNW 11 1900 (1100) 85 55 1015.2 W12 79 53 1019.2 NE 18 2000 (1200) 83 57 1014.2 WSW 12 80 52 1018.2 NE 17 2100 (1300) 96 44 1012.5 S4 81 53 1017.2 NNE 18 2200 (1400) 95 43 1011.9 NNW 12 73 59 1016.9 W16 2300 (1500) 92 44 1012.2 N12 74 60 1016.5 WNW 13 0000 (1600) 90 45 1012.2 N12 67 60 1016.4 W11 0100 (1700) 85 47 1012.2 N9 64 59 1016.6 W5 0200 (1800) 81 48 1012.5 NW 10 60 58 1017.1 W4

Unlike the July event, the highest hourly temperature occurrence of a Sundowner with north-northeast ¯ow here occurs much closer to its time of occurrence on a at Santa Maria indicates that onshore ¯ow of cool ma- typical (i.e., non-Sundowner) day. Thus Sundowner rine air at Santa Maria is not a necessary condition for events may not always be well de®ned on the basis of a Sundowner event to occur, despite its apparent pres- the timing of the maximum temperature as suggested ence in the vast majority of cases. by Ryan and Burch (1992). Another difference from the July case is the signi®- Also in contrast to the July case are the offshore winds cant northwesterly ¯ow at 500 mb (Fig. 8). Similar to and warming observed at Santa Maria as the Sundowner the earlier case, however, is the presence of backing develops in Santa Barbara. As these stations are quite winds between the 850- (Fig. 9) and 500-mb levels, near each other, the contrast in temperature between the which according to the thermal wind relation is indic- two locations gives some measure of the added degree ative of cold advection in the intermediate layer. Cold of warming that occurs at Santa Barbara as a result of advection is also evident at the 850-mb level itself. the mountains immediately to its north. In addition, the The surface analysis for the same time (Fig. 10) shows

FIG. 8. NCEP 500-mb analysis for 0000 UTC 3 November 1992. FIG. 9. NGM 850-mb analysis for 0000 UTC 3 November 1992.

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FIG. 10. NCEP surface analysis for 0000 UTC 3 November 1992. Conventions as in Fig. 5. Report from Santa Barbara indicated by a box.

a strong northwest±southeast-oriented pressure gradient extending the length of California. Similar to the July 1992 case, sea level pressure to the north of Santa Bar- bara, both along the coast and in the central interior of the state, are signi®cantly higher than at Santa Barbara itself. The 0000 UTC 3 November sea level pressure difference between SMX and SBA, for example, is 4.2 mb (Fig. 10 and Table 2). Unlike the July 1992 event, however, sea level pressures at SBA are still higher (albeit just slightly) than at coastal locations to the southeast (Fig. 10). The VBG sounding for 0000 UTC 3 November 1995 is shown in Fig. 11. Although the sounding contains obvious errors (most notably the temperature and dew- point pro®les in the 550±600-mb layer; also the surface layer where an excessive superadiabatic lapse rate is shown adjacent to the ground), it is still useful in anal- ysis of this Sundowner event. Most notably, in com- parison with the July 1992 event, no signi®cant inver- FIG. 11. VBG sounding for 0000 UTC 3 November 1992. (Note: sounding reproduced as received from NCEP despite obvious errors; sion appears near the surface [with the exception of the see text for further discussion.) likely erroneous thin very stable layer just above the

Unauthenticated | Downloaded 09/27/21 04:21 AM UTC SEPTEMBER 1998 BLIER 711 depicted (and also likely erroneous) superadiabatic sur- road obstructing traf®c ¯ow, as well as several telephone face layer]. However, in this case a signi®cant stable poles that were snapped in half. layer extends from 855 to 885 mb, which is just above At 2100 PST 31 December, the of®cial temperature the top of the Santa Ynez Mountains, with a weaker report from SBA was 68ЊF (20.0ЊC), with a dewpoint stable layer above. A wind maximum appears at the of 36ЊF (2.2ЊC), and a northwest wind of 23 kt (11.8 base of this stable layer, with ¯ow out of the north- msϪ1) with gusts to 35 kt (16.0 m sϪ1). One hour later, northeast at 45 kt (23.2 m sϪ1). Thus there is much the reported temperature was 70ЊF (21ЊC), with a dew- stronger ¯ow perpendicular to the mountains than in the point of 32ЊF(0ЊC), and winds from the north at 29 kt July case, along with a stable layer at the appropriate (14.9 m sϪ1) with gusts to 44 kt (22.7 m sϪ1). Unfor- level for mountain wave development (Queney et al. tunately, there were several missing surface observation 1960). In order to account for the high temperature of reports during the period of this event from both Santa 98ЊF (36.7ЊC) at SBA, air would have to descend from Maria and Santa Barbara. However, at 2300 PST, Santa approximately the 780-mb level, or well above the top Maria reported a temperature of 59ЊF (15.0ЊC) and a of the Santa Ynez Mountains, indicating signi®cant dewpoint of 42ЊF (5.6ЊC), with a wind out of the east mountain wave activity. Unlike the July 1992 case, al- at 13 kt (6.7 m sϪ1). As in the November 1992 event, ternative explanations for the high temperature appear even in the presence of offshore ¯ow at both locations, less plausible. In November, the degree of superadi- the temperature was signi®cantly cooler at Santa Maria abatic warming of the surface layer is expected to be than at Santa Barbara. small; likewise any surface air transported from the Interestingly, at the times of the preceding Santa Bar- windward side of the mountains is unlikely to experi- bara reports, sky conditions in the Santa Barbara area ence signi®cant warming from surface sensible heat were reported as ``partly cloudy.'' Periodic personal ob- ¯uxes and thus little mitigation of the adiabatic cooling servation by the author from approximately 2115 to during its ascent to the level of the ridgetop. In fact, 2300 PST 31 December indicated the presence of a the high temperature at Lake Cachuma on 2 November single linear stationary lenticular cloud approximately 1995 was only 82ЊF (27.8ЊC), or 15ЊF (8.3ЊC) less than 10 km to the lee of the Santa Ynez Mountains and at Santa Barbara [compared to 8ЊF (4.4ЊC) less in the oriented parallel to the mountain range (no other clouds July case]. Thus in the present case mountain wave de- were evident). An observation made soon after the end velopment alone would appear to provide a plausible of the signi®cant wind episode revealed clear skies. explanation for the anomalously warm temperature ob- The NCEP surface analysis for 0000 UTC 01 January served at Santa Barbara. 1996 (1600 PST 31 December 1995) (Fig. 12) shows a strong north-northwest to south-southeast pressure gra- dient across the state of California. Unlike the preceding 5. The 31 December 1995 Sundowner event two cases, the difference in sea level pressure between In this event temperatures were signi®cantly more SBA and SMX is only 3 mb, and the pressure at SBA moderate than in the two episodes described above, but is signi®cantly higher than at coastal locations farther wind speeds reached damaging levels. A statement is- to the south. It should be noted, however, that this Sun- sued by the National Weather Service Forecast Of®ce downer wind episode initiated several hours after the in Oxnard at 0645 UTC 1 January 1996 (2245 PST 31 0000 UTC analysis time, rather than signi®cantly earlier December 1995) noted that in the coastal areas of Santa in the day as in the other two cases. The surface analysis Barbara County ``several roads were closed due to de- also shows the tail end of a ``back door'' cold front bris cluttering the streets'' and that ``wind speeds of 40 approaching southern California from the northeast; to 45 mph with gusts to near 60 mph were reported by pressure rises are evident behind the front while pressure several residents in the Santa Barbara area.'' An As- falls are occurring ahead of it. sociated Press wire report dated 1 January 1996 indi- The corresponding 850-mb analysis (Fig. 13) indi- cated that ``hundreds of trees blew down onto roads, cates strong north-northeasterly geostrophic ¯ow in the cars, and buildings'' and that ``live power lines lay in vicinity of Santa Barbara, while Vandenberg AFB is some roads.'' The report goes on to say ``strong windsÐ reporting northerly winds at 40 kt (20.6 m sϪ1). A region measured between 50 and 60 mph at Santa Barbara Har- of signi®cant cold advection is evident beginning sev- borÐcaused several traf®c accidents resulting in minor eral hundred kilometers upstream. Consistent with this injuries'' and, according to a local ®re captain, ``wind cold advection, backing of the geostrophic ¯ow occurs also smashed windows of shops and restaurants on Santa between the 850- and 500-mb levels. At Vandenberg Barbara's wharf.'' A number of boats in Santa Barbara AFB, the observed 500-mb wind direction (Fig. 14) is Harbor were reported to have broken free of their moor- the same as that at 850 mb, but with the wind speed ings, while an Amtrak train was blocked by downed increased to 65 kt (33.5 m sϪ1). The geopotential height trees. The author of this paper, who happened to be of 581 dm is quite high for the location and time of entering the Santa Barbara area from the east on U.S. year, as is the 500-mb temperature of Ϫ10ЊC. Highway 101 at 2130 PST 31 December, encountered Signi®cant additional information on the vertical a number of large trees (length Ͼ12 m) down on the structure of the atmosphere just prior to the initiation

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FIG. 12. NCEP surface analysis for 0000 UTC 01 January 1996. Conventions as in Fig. 5. Report from Santa Barbara indicated by a box. of the wind event is evident from the 0000 UTC 1 phenomenon considered here, several additional com- January 1996 VBG sounding (Fig. 15). Three key fea- plications arise. First, lack of a robust historical database tures appear in this sounding: a strong stable layer at of surface observations at locations adjacent to or on approximately the 850-mb levelÐand thus just above the mountain slope itself limits the analysis to just con- the top of the Santa Ynez Mountains, a lower-tropo- sideration of those cases that are suf®ciently intense to spheric jet with wind speeds reaching 75 kt (38.6 m impact conditions near the coast, and even then, as noted sϪ1) at about the 710-mb level (the maximum wind by Ryan (1996), not necessarily where the strongest speed between the surface and the tropopause), and (al- effect is typically observed. Second, there are really two beit modest) backing of the wind above this level, re- somewhat different forecast concerns that arise in as- sulting in further reduction of the magnitude of the sociation with these Sundowner events: the potential for cross-mountain component of the ¯ow. strong winds and the potential for very warm temper- atures. In the July 1992 case, for example, very high temperatures occurred on the coastal plain but associ- 6. Discussion ated wind speeds were quite modest. In contrast, the A number of different dynamical mechanisms have December 1995 event brought winds of destructive been proposed to explain downslope windstorms. These force but temperatures were no more than pleasantly have, however, generally been derived using simpli®ed mild for a midwinter evening. Finally, the mountain theory, atmospheric structures, and terrain pro®les and barrier formed by the Santa Ynez Mountains does con- thus their degree of applicability to the speci®c and more tain some signi®cant canyons and passes and thus the complex circumstances associated with a particular ob- potential for strong local channeling of the downslope served event is unclear. With respect to the Sundowner wind exists (Ryan 1992).

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FIG. 13. NCEP 850-mb analysis for 0000 UTC 1 January 1996. FIG. 14. NCEP 500-mb analysis for 0000 UTC 1 January 1996.

Linear mountain wave theory should be reasonably synoptic-scale pressure gradient is in phase with the applicable to those cases in which wind speeds, both wave-induced pressure gradient. upstream and aloft (e.g., in the VBG sounding) and The July 1992 case satis®es the ®rst two of the above downwind on the coastal plain, remain modest (with, criteria, but apparently not the third (assuming that the again, the caveat that conditions at SBA might not al- VBG sounding is representative of the upstream tem- ways be representative of those at other locations near- perature pro®le). In this case, then, it would seem plau- by). Within this framework, three key criteria were de- sible that the very warm temperatures observed near the scribed by Queney et al. (1960) and Klemp and Lilly coast at Santa Barbara were produced by a combination (1975). First, the mountain barrier causing the event of simple advective transport of hot surface air from the should have a steep lee slope. Signi®cant theoretical valley upwind of the Santa Ynez Mountains, strong sur- work by Smith (1979) and Lilly and Klemp (1979) with- face diabatic heating, and erosion of the marine bound- in an inviscid framework showed that asymmetric ary layer allowing downward penetration of the very mountains, with a steep leeward slope and a gentle warm air above. windward slope, functioned best at generating large- In the November 1992 case, however, a signi®cant amplitude mountain waves. Subsequent numerical sim- stable layer is evident just above the level of the moun- ulation with inclusion of surface friction, however, not only produced more realistic results in general (Richard et al. 1989) but also suggests that it is just the steepness of the lee slope that is of signi®cance (Miller and Durran 1991). Second, throughout a deep layer of the tropo- sphere, the wind should be directed signi®cantly across the mountain barrier (within 30Њ of perpendicular to the ridge line), with the wind speed increasing with height and exceeding 7±15 m sϪ1 at the crest (values depending on the height and shape of terrain). Third, the upstream temperature pro®le should show a strongly stable layer near the mountaintop level, with weaker stability above. [Weaker stability below the inversion seemed to also favor lee wave development to the east of the Sierra Nevada (Colson 1954).] Finally, Durran (1986) notes that strong downslope winds are more likely when the FIG. 15. VBG sounding for 0000 UTC 1 January 1996.

Unauthenticated | Downloaded 09/27/21 04:21 AM UTC 714 WEATHER AND FORECASTING VOLUME 13 tain crest; here, then, all of the aforementioned criteria ered in this paper is no longer readily obtainable). In appear to be satis®ed and thus mountain wave devel- particular, we examined 18-h output from the model opment is suggested. Also in contrast to the July case forecast initialized at 1200 UTC 31 December 1995 (and consistent with the presence of mountain waves) (valid at 2200 PST 31 December; not shown). Although is the lack of a plausible mechanism to account for the the large-scale structure of the surface, 850-, and 500- very high temperatures observed at SBA other than mb ¯ow appeared well predicted, mesoscale detail of downward transport of air from a level signi®cantly the Sundowner event was entirely absent, as would be above that of the mountain crest. As in the July 1992 expected given the very small horizontal scale of the event, offshore winds at SBA were of only modest mag- Santa Ynez Mountains. nitude. Assuming, then, that operational model output is ca- In the December 1995 case, however, a very strong pable of accurately forecasting the larger-scale wind and downslope wind event clearly occurred, thus indicating thermal structure of the atmosphere in the region in the likely development of large-amplitude mountain which these Sundowners occur, some guidance can be waves and therefore the need for consideration of the provided to the operational forecaster. During the sum- fully nonlinear dynamics. Durran (1990) discusses three mer season, one should be alert for the possibility of different possible mechanisms for the production of se- anomalously warm temperatures on the coastal plain vere downslope winds: 1) the development of super- whenever sea level pressure at Santa Barbara is lower critical ¯ow in a hydraulic jump, 2) the generation of than that in the central interior of California and sig- large-amplitude vertically propagating mountain waves, ni®cantly lower than at Santa Maria [for the latter, Ryan and 3) the development of a wave-induced critical layer. (1996) proposes a minimum of 1.8 mb, while Finke Durran concludes that the ®rst of these mechanisms ap- (1990) suggests a minimum of 2.5 mb between Santa pears to offer the best dynamical description for down- Maria and Los Angeles with even lower sea level pres- slope windstorms but, unfortunately, is not easily ap- sure at Santa Barbara], and the 850-mb-level ¯ow has plied in practical forecasting due to the number of rather a signi®cant cross-mountain (i.e., northerly) component. different physical circumstances that could potentially The shallower the marine inversion layer, the warmer result in a transition from subcritical to supercritical the air just above, and the higher the surface air tem- ¯ow. peratures in the Santa Ynez Valley upwind of the moun- Results of a recent three-dimensional high-resolution tains, the greater the potential for very high temperatures nonhydrostatic modeling study of windstorms along the to occur under such circumstances. In essence, these western side of the Washington Cascade Mountains cases seem to represent the migration of typical warm (Colle and Mass 1998) suggest that intense windstorms season interior weather conditions to the more com- in the foothills of the lee slope of these mountains are monly marine-air-dominated coastal plain. Although associated with the combination of strong cross-barrier temperatures at Santa Barbara are thus dramatically ¯ow and an environmental critical level (i.e., a level at higher than those usually experienced, they are gener- which there is no cross-barrier ¯ow) or layer of reverse ally comparable to those typically observed during the shear (cross-barrier winds decreasing with height) in the summer at low elevations in the interior of the state (as lower to middle troposphere. The magnitude of the sim- is evident from Fig. 5). ulated windstorm increased if, in addition to the above, Anomalously very warm temperatures can also occur a moderately shallow strongly stable layer existed just during other times of the year, as evidenced by the No- above the mountain crest with reduced stability at higher vember 1992 event. In these cases, though, temperatures levels. above the boundary layer and in the interior are typically All of these conditions were satis®ed in the December much lower than in the summer months and thus sub- 1995 Sundowner event. However, general applicability sidence from well above the mountaintop level is nec- of these ®ndings to the Sundowner winds of the Santa essary. This implies mountain wave development, as Barbara region may be mitigated by signi®cant differ- previously discussed. Here, then, the forecaster would ences in the topography, especially the comparatively want to be alert for the combination of the sort of pres- much larger width of the Cascades and the presence of sure gradient and 850-mb ¯ow described above with a a signi®cant gap in that mountain range. In addition, layer of enhanced stability in the VBG sounding at or both previous theoretical studies and the numerical sim- slightly higher than the level of the mountain crest. The ulations of Colle and Mass (1998) more thoroughly ex- occurrence of a stable layer well above the typical top amine the in¯uence of a tropospheric critical level than of the marine boundary layer in conjunction with north- that of a layer of reverse shear. While the former is erly ¯ow aloft is most likely to occur in association with present in most signi®cant Cascade Mountain wind an elevated frontal zone and, thus, after the passage of storm events, this is not the case for the Sundowner a surface cold front. winds of Santa Barbara. Infrequently, an elevated stable layer (i.e., one ex- Operational Eta Model numerical output was exam- tending above the mountaintop level) in association with ined for the December 1995 case (corresponding op- signi®cant northerly ¯ow might occur in one of the sum- erational model output for the other two events consid- mer months when the temperature inland and just above

Unauthenticated | Downloaded 09/27/21 04:21 AM UTC SEPTEMBER 1998 BLIER 715 the stable layer tends to be at its warmest. The potential served in the November 1992 case, while the latter may resulting combination of a very warm air mass and have played a signi®cant role in the July 1992 case. mountain wave development could conceivably produce In the December 1995 case, by contrast, the wind the sort of extraordinary high temperature described in manifestation was of far greater signi®cance than the the introductory section of this paper. Cursory exami- associated warming. In this Sundowner event, wind nation suggests the 27 June 1990 Sundowner was such speeds reached destructive magnitudes and caused sig- an event. On this day the maximum temperature at Santa ni®cant damage in the Santa Barbara area. This event Barbara airport was 109ЊF while the temperature at El also started in the early evening hours, rather than mid- Capitan Beach 11 miles (17.7 km) farther west reached day to early afternoon as in the other two cases. 116ЊF; winds of 30 mph (13.4 m sϪ1) were reported at Much further work is needed, however, on this fas- the airport at 1548 PDT and wind gusts to 60 mph (26.8 cinating and heretofore relatively unexamined meso- msϪ1) occurred within the city of Santa Barbara (Ryan scale topographic phenomenon. In particular, acquisi- 1996). tion of much higher resolution surface and upper-air data Whenever there is both strong cross-mountain ¯ow during a Sundowner wind event would contribute sig- and a strong mountaintop stable layer (a combination ni®cantly to our understanding of the processes respon- most likely to occur during the cool season months), sible for the associated very high temperatures (and the possible development of a signi®cant wind event on sometimes accompanying strong winds). As just one the coastal plain needs to be considered. It would appear example, there is at present little in the way of obser- that the potential for a severe windstorm event is en- vational data to enable de®nitive examination of the hanced if the high wind speeds upstream extend down possible in¯uence of the nearby, higher, and larger-scale to low levels, the stable layer is relatively shallow with Sierra Madre and San Rafael Mountains on these events. a layer of signi®cantly reduced stability above, and a It is conceivable, for example, that mountain wave de- layer of reverse shear is evident in the lower to middle velopment from these ranges could affect conditions in troposphere. the Santa Barbara area; the barrier formed by these mountains could also act to block onshore ¯ow and divert it to the west with the result of enhanced low- 7. Summary level ¯ow over western Santa Barbara county. Mesoscale modeling studies are also needed, both to A mesoscale region of the California coast in the further understanding of these Sundowner wind and vicinity of Santa Barbara occasionally experiences ex- warming events, and to examine their relationship to traordinarily warm temperatures and signi®cant down- the development of the Catalina eddy. Numerical sim- slope winds in association with lower-tropospheric ¯ow ulation of the December 1995 event has been performed over the abruptly rising Santa Ynez Mountains to its and will be reported on in a subsequent paper; prelim- north. Synoptic overviews of three such cases of Sun- inary results can be found in Blier and Ma (1997). As downer wind events have been presented, along with extraordinarily warm temperatures, strong and some- consideration of possible physical mechanisms respon- times damaging winds, and a number of destructive ®re- sible for the observed occurrence of high temperatures storms have been associated with these Sundowner and/or strong winds. winds, improvement in our understanding and fore- In the cases considered here, as well as in others casting capability of these events is essential. examined in a more cursory fashion by the author, sig- ni®cant perpendicular ¯ow at the ridgetop level of the Acknowledgments. The author gratefully acknowl- Santa Ynez Mountains is present. The predominant re- edges the assistance with data provided by John Oleska, sulting surface ¯ow in the vicinity of Santa Barbara on Fabrice Cuq, and James Murakami, and thanks Prof. the narrow coastal plain to the lee of the mountains is Arnold Court for providing a copy of the Davidson ar- thus offshore, precluding the signi®cant and more typ- ticle. Perceptive comments and suggestions provided by ical cool marine in¯uence. In the July 1992 case (and three anonymous reviewers improved the presentation perhaps to a more limited degree in the November 1992 of this paper. This research was sponsored in part by case), some of the warming is thus likely a consequence Grant CS-88-92 of the California Space Institute. of the greater diurnal heating enabled in the absence of a sea breeze. In order to account for the very high tem- peratures sometimes observed, however, other processes REFERENCES are necessary. In particular, signi®cant warming can be Blier, W., and Q. 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istics of past events and three-dimensional idealized simulations. southern Oregon and northern California. Wea. Forecasting, 2, Mon. Wea. Rev., 126, 53±71. 253±258. Colson, D., 1954: Meteorological problems in forecasting mountain Miller, P. P., and D. R. Durran, 1991: On the sensitivity of downslope waves. Bull. Amer. Meteor. Soc., 35, 363±371. windstorms to the asymmetry of the mountain pro®le. J. Atmos. Davidson, G., 1869: Coast Pilot of California. United States Coast Sci., 48, 1457±1473. Survey, U.S. Government Printing Of®ce, 262 pp. Queney, P., G. Corby, N. Gerbier, H. Koschmieder, and J. Zierep, Durran, D. R., 1986: Mountain waves. Mesoscale Meteorology and 1960: The air¯ow over mountains. WMO Tech. Note 34, 135 Forecasting, P. S. Ray, Ed., Amer. Meteor. Soc., 472±492. pp. [Available from World Meteorological Organization, P.O. , 1990: Mountain waves and downslope winds. Atmospheric Pro- Box 2300, CH-1211 Geneva 2, Switzerland.] cesses over Complex Terrain, Meteor. Monogr., No. 45, Amer. Richard, E., P.Mascart, and E. C. Nickerson, 1989: The role of surface Meteor. Soc., 59±81. friction in downslope windstorms. J. Appl. Meteor., 28, 241± Finke, B. W., 1990: Sundowner winds and the June 25±28 1990 Santa 251. Barbara ®re. NOAA/NWS Western Region Tech. Attachment Ryan, G., 1994: Climate of Santa Barbara, California. NOAA Tech. No. 90-30, 4 pp. [Available from National Weather Service, Memo. NWS WR-225, U.S. Department of Commerce, 86 pp. Western Region, Salt Lake City, UT 84147.] [Available from National Technical Information Service, U.S. Gomes, D., O. L. Graham Jr., E. H. Marshall, and A. J. Schmidt, Dept. of Commerce, Sills Building, 5285 Port Royal Rd., Spring- 1993: Sifting Through the Ashes: Lessons Learned From the ®eld, VA 22161.] Painted Cave Fire. South Coast Historical Series, Graduate Pro- , 1996: Downslope winds of Santa Barbara, California. NOAA gram in Public Historical Studies, University of California, Santa Tech. Memo. NWS WR-240, U.S. Department of Commerce, 44 Barbara, 194 pp. pp. [Available from National Technical Information Service, Huschke, R. E., Ed., 1959: Glossary of Meteorology. Amer. Meteor. U.S. Dept. of Commerce, Sills Building, 5285 Port Royal Rd., Soc., 638 pp. Spring®eld, VA 22161.] Klemp, J. B., and D. K. Lilly, 1975: The dynamics of wave-induced , and L. E. Burch, 1992: An analysis of Sundowner winds: A downslope winds. J. Atmos. Sci., 32, 320±339. California downslope wind event. Preprints, Sixth Conf. on Lilly, D. K., and J. B. Klemp, 1979: The effects of terrain shape on Mountain Meteorology, Portland, OR, Amer. Meteor. Soc., 64± nonlinear hydrostatic mountain waves. J. Fluid Mech., 95, 241± 67. 261. Smith, R. B., 1979: The in¯uence of mountains on the atmosphere. Mass, C. F., 1987: The ``Banana Belt'' of the coastal regions of Advances in Geophysics, Vol. 21, Academic Press, 87±230.

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