Last month was the driest ever September in Los Angeles County. Now come the Santa Ana winds
By Allison Chinchar, CNN Meteorologist
After the hottest and driest summer in California history, and a September that was Los Angeles County’s driest ever, concerns are high that Santa Ana wind season could significantly worsen what has already been a disastrous fire year.
For the second time this week, Pacific Gas & Electric has had to execute planned power outages due to strong winds. PG&E issued the power shut-off warning for nearly a dozen counties in an effort to help prevent wildfires from sparking.
New fires are not the only concern. There are fears that high winds will fan existing fires such as the Alisal Fire, which has closed part of Highway 101 and Amtrak railways in Santa Barbara County. The strong winds could not only trigger further power outages but also hinder firefighting progress.
“Gusty Santa Ana winds are expected Friday and Saturday in Los Angeles and Ventura Counties,” said the National Weather Service in Los Angeles/Oxnard on Thursday. “The dry, warm and windy conditions will bring dangerous fire weather conditions to the majority of LA and [Ventura] counties.”
Santa Ana winds are strong, hot, dust-bearing winds that descend toward the Pacific Coast around Los Angeles from inland desert regions.
The weather condition is most common from October through March, when the desert is relatively cold. The winds develop as high pressure builds over Nevada’s Great Basin, according to the UCLA Department of Atmospheric and Oceanic Sciences.
What makes matters worse is that California is coming off its worst drought on record.
Carol Smith, a meteorologist with the National Weather Service, says that one risk with existing fires is that Santa Ana winds can lead to extreme fire behavior, which includes fire whirls and pyrocumulus clouds, which can produce lightning and thunder.
“Fuel moisture is very low, which means those fuels are ready. If there’s any kind of spark, or something to start a fire, those fuels are primed and ready to just take off,” Smith said.
In the wake of a hot, dry summer, the absence of rain could prove disastrous.
“The fires can grow 1,000 acres in one hour, so it is critical to get suppression ASAP, especially in Santa Ana dry wind and warm conditions,” said Alex Tardy, the warning coordination meteorologist with the NWS in San Diego. “The summer of 2021 was the warmest on record for mountains and deserts, so that is much extra stress on the vegetation. The winter of 2020-21 was about 40 to 50% of average rainfall (dry water year), so that also adds to more stress and drying of fuels (live or dead fuels).”
The water year — a 12 month period during which precipitation totals are measured — runs from October 1 to September 30, and this past water year was not kind to California.
California relies on weather events called atmospheric rivers — narrow regions in the atmosphere that transport water vapor — to provide much needed water to reservoirs, lakes and agriculture. This past year was dismal, with only two of these strong events occurring in Southern California. The region normally averages seven per year.
The bigger concern is what the future holds.
La Niña is expected this winter, which does not usually bode well for Southern California. In a typical La Niña winter, most of the Southern United States has drier- and warmer-than-average conditions. This could mean the drought-stricken Southwest will likely stay drier.
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