Extreme winds and fire weather in coastal Santa Barbara County, CA: An observational analysis

Abstract

Coastal Santa Barbara (SB) County in Southern California, characterized by a Mediterranean climate and complex topography, is a region prone to downslope windstorms that create critical fire weather conditions and rapidly spread wildfires. The Santa Ynez Mountains, oriented from east to west, rise abruptly from the coast, separating air masses from the ocean and the Santa Ynez Valley. The juxtaposition of these geographic features generates spatiotemporally variable wind regimes. This study analyzes diurnal-to-seasonal wind cycles and extremes in this region using hourly data from eight weather stations and four buoys for the period 1998-2019. Data from a vertical wind profiler at the Santa Barbara airport in Goleta, CA was extracted from August 2016 to September 2020. Air temperature, dew point temperature, and the Fosberg fire weather index are examined at land stations. We show that cycles in wind speed vary spatiotemporally; mountain (valley and coastal) stations exhibit a pronounced semiannual (annual) cycle, and wind maxima is observed during the evening (afternoon) at mountain (valley and coastal) stations. Differences in wind speed percentiles were evident among stations, particularly at and above the 75th percentile. Strong winds recorded at buoys were significantly correlated (between r = 0.3-0.5) to land stations. However, cross-correlational analysis did not reveal any temporal lags between mountain stations and buoys. Distributions of temperature and dew point during extreme winds differed between east and west mountain stations. Significant fire weather conditions were most frequent at mountain stations in Refugio and Montecito, with 5% occurrence in the spring and over 3% occurrence in fall. Weaker summertime winds lowered fire weather conditions at Montecito in the summer.extreme winds, fire weather, Mediterranean climate, mountain winds, Southern California, Sundowner winds, thermally driven circulations | INTRODUCTIONCoastal Southern California is characterized by a Mediterranean climate, with dry summers and wet winters. Nonetheless, regional differences in climate are attributed to the complex terrain spanning the U.S. West Coast. Santa Barbara (SB) County, situated in Southern California, provides an example of a region where

Spatial–Temporal Analysis of a Summer Heat Wave Associated with Downslope Flows in Southern Brazil: Implications in the Atmospheric Boundary Layer

“…Therefore, the temporal variability of the dew point is an important signature of the presence of a DW. Conditions similar to those described above have also been observed in DWs, known as Sundowners, along the coast of Santa Barbara, California [59].…”

Wildfire Risk in the Complex Terrain of the Santa Barbara Wildland–Urban Interface during Extreme Winds

“…However, during critical fire weather conditions, wind is the dominant factor in determining fire spread [20,21]. In coastal Santa Barbara County, the most critical fire weather is often associated with downslope windstorms on the slopes of the Santa Ynez Mountains (SYM), known as Sundowner winds or Sundowners [22][23][24]. Sundowners occur year-round [23] and may create critical fire weather conditions as the strong, northerly dry winds rapidly spread fires southward toward highly populated areas (Figure 1a) [25][26][27][28][29].…”

“…Although a decrease in relative humidity and temperature increases are casedependent [22,24,26], Sundowners often create critical fire weather conditions due to gusty winds and a lowered dew point [25,30]. The strongest winds are observed along the middle of the SYM mountain slopes, though strong winds may extend into the foothills and onto the coastal plain [23,24,26,27].…”

“…Although a decrease in relative humidity and temperature increases are casedependent [22,24,26], Sundowners often create critical fire weather conditions due to gusty winds and a lowered dew point [25,30]. The strongest winds are observed along the middle of the SYM mountain slopes, though strong winds may extend into the foothills and onto the coastal plain [23,24,26,27]. One study [23] utilized a combined empirical orthogonal function analysis on the zonal and meridional winds from a 30-year Weather Research and Forecasting (WRF) model simulation at 1 km grid resolution [32].…”

“…Some of these wildfires have crossed these major routes, such as the Painted Cave (1990), Tea (2008), Jesusita (2009), Sherpa (2016), Thomas (2017), Cave (2019), and Alisal (2021; not shown) fires have come close (Figure 1a). Although a decrease in relative humidity and temperature increases are casedependent [22,24,26], Sundowners often create critical fire weather conditions due to gusty winds and a lowered dew point [25,30]. The strongest winds are observed along the middle of the SYM mountain slopes, though strong winds may extend into the foothills and onto the coastal plain [23,24,26,27].…”