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 37.88C (1008F). 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 s21 (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 q 1998 American Meteorological Society Unauthenticated | Downloaded 09/27/21 04:21 AM UTC SEPTEMBER 1998 BLIER 703 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 5 500 m, solid line 5 1000 m, and hatched regions .1500 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 758 and along limited segments of the coast of southern Oregon 808, 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 1338F, and continued at or near that point for nearly itself, can well exceed 1008F (37.88C). 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 1228, and at seven it stood at 778.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 1001 year period of standardized temperature of 1098F (42.78C), 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 658F (18.38C)]. 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 1308F'' 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.