Sundowner winds

A sundowner is a northerly offshore wind in California along the southern Pacific slope of Santa Ynez Mountains, in communities along the Gaviota Coast, Santa Barbara, and Montecito.

Formation

It occurs when pressure gradients create conditions for northerly, offshore winds across the east-west oriented Santa Ynez Mountains. The winds blow with greatest force when the pressure gradient is perpendicular to the axis of the Santa Ynez Mountains, which rise directly behind Santa Barbara and separates the cool Pacific Ocean from the Santa Ynez Valley.

Sundowner winds may occur year-round but their frequency increases during Spring. The National Weather Service (LA/Oxnard office) recognizes three types of Sundowner Winds: a) Western Sundowners (with dominant north-northwesterly winds) that typically affect the western side of the Santa Ynez Mountains, and coastal areas of Gaviota and Refugio (often referred to as "Gaviota" type); b) Eastern sundowners (with dominant north-northeasterly winds) that typically affect the eastern portion of the Santa Ynez Mountains, and eastern coastal areas of Santa Barbara and Montecito (also known as Montecito type); c) hybrid regime, in which both western and eastern Sundowners are observed in the same evening.[1]

Although Eastern Sundowners are more frequent during Spring, a secondary peak is observed during Fall, when they may precede Santa Ana events by a day or two as it is normal for high-pressure areas to migrate east, causing the pressure gradients to shift to the northeast.[2] Although Sundowners are typically nighttime events that terminate after sunrise, they may repeat for days, while Santa Anas are multi-day long events. Sundowners often occur without an associated Santa Ana event and has no clear links with other downslope windstorms in the Central Coast.[1]

Fire dangers

Sundowners are particularly dangerous during wildfire season because the air heats and dries as it descends from the mountains to the sea. Gale force hot, dry winds can make firefighting impossible.[3]

Sundowners have been related to many significant wildfires that spread toward coastal communities in Santa Barbara. The Painted Cave Fire in June 1990, the Tea House Fire in November 2008, the Jesusita Fire in May 2009, the Sherpa Fire in June 2016, the Holiday Fire in July 2018, the Cave Fire in November 2019, the Alisal Fire in October 2021 are some examples. The Painted Cave fire, the Jesusita Fire and the Tea-house fire were among the most destructive wildfires in the region.

A sundowner quickly burned a swath from the mountains through populated areas and across Highway 101 into Hope Ranch during the 1990 Painted Cave Fire.

The most intense periods of the Jesusita Fire's destruction have also been blamed on sundowner winds. The Sherpa Fire grew to 4,000 acres (1,600 ha) overnight due to the sundowner winds, destroying the water system for El Capitán State Beach at the beginning of the 2016 fire season.[4]

Origin

The etymology of the word sundowner is uncertain, but some speculate that the name derives from the Spanish term zonda, or from the Arabic simoom, which are both similar wind phenomena.[5] However, the origin of the name is more likely linked to the fact that that sundowner winds commence in the evening near sunset, when stability increases over mountain top and slopes, the onshore sea breezes abate and offshore flows such as the sundowners pick up.

Temperature inversion

As sundowner events typically happen near nighttime or during nighttime, when coastal temperatures die down, there can be a sharp temperature difference in monitoring stations merely blocks away, due to elevation difference. Higher elevations of hills can correlate with huge temperature rises compared with lower elevations, and can rival those seen in daytime heatwaves --- coastal inversion layer kept beaches (Pacific side of San Francisco) some 40 to 45 degrees fahrenheit cooler than hills at 2500 or 5000 feet (Mount Tamalpais) on afternoon of July 6, 2024. Sundowners have caused similarly intense sharp temperature contrasts akin to these daytime inversion layers, but surprisingly at close to midnight, where California State Route 192 approximates the hot vs cool dividing line, in the Santa Barbara area.

See also

References

  1. ^ a b Jones, C.; Carvalho, C.; Duine, G.J.; Zigner, K. (2021). "Climatology of Sundowner winds in Coastal Santa Barbara, California, based on 30-yr high resolution WRF downscaling". Atmospheric Research. 249 (10530) 105305. Bibcode:2021AtmRe.24905305J. doi:10.1016/j.atmosres.2020.105305. Retrieved June 18, 2026.
  2. ^ Ryan, G., and L. E. Burch, 1992. An analysis of sundowner winds: A California downslope wind event. Preprints, Sixth Conf. on Mountain Meteorology, Portland, Oregon, Amer. Meteor. Soc., 64–67.
  3. ^ Tasoff, Harrison (August 15, 2019). "UCSB Scientists to Study Sundowner Winds". Edhat. UCSB. Retrieved January 13, 2020.
  4. ^ Serna, Joseph; Fernandez, Alexia (June 17, 2016). "Santa Barbara County declares state of emergency after wildfire grows to 4,000 acres overnight". Los Angeles Times. Retrieved June 17, 2016.
  5. ^ Pine, Stephen J. (2016). California: A Fire Survey. Tucson: University of Arizona Press. p. 66. ISBN 978-0816532612.
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