The winds follow several days of record-breaking heat that has amplified fire danger, particularly in Southern California, which saw temperatures soar into the 80s and 90s in the middle of a largely dry winter.
The high winds alone, with gusts to 80 to 90 mph in the hills of Los Angeles and Ventura counties and up to 70 mph in some valley locations, are likely to cause significant disruptions in the form of power outages and downed trees.
“Significant wind impacts will be likely with this event, including the threat of widespread downed trees and power lines, as well as power outages,” the National Weather Service forecast office in Los Angeles stated in an online forecast discussion Monday. While humidity levels may be high enough to avoid the most dire fire weather conditions, the dryness of the area’s vegetation plus the winds may make for an especially risky period from Monday night through Wednesday morning.
High wildfire risk in Southern California means the added burden of preemptive power shut-offs to prevent electrical ignitions. Southern California Edison, the utility that serves Los Angeles and surrounding counties, could cut power to 243,725 customers, it warns, a number that could vary throughout the day Monday as the forecast evolves. The potential shut-offs and outages come amid a prolonged coronavirus surge — the region’s worst since the start of the pandemic — in which thousands are hospitalized, intensive care units are over capacity, and a stay-at-home order remains in place.
This week’s menacing weather can be traced to an area of low pressure setting up just off the California coast, along with high surface pressure building into the Rockies and Great Basin. The pressure difference (air flows from high to low pressure) is powering high winds blowing from land-to-sea, or offshore, across California. These winds are expected to strengthen Monday night and into Tuesday in most locations.
High fire risk in Southern California
A dangerous combination of very strong winds and extremely dry vegetation is bringing rare levels of midwinter fire risk to Central and Southern California. Forecasters issued Red Flag Warnings for “critical” fire weather conditions in Los Angeles, Ventura, Santa Barbara and San Luis Obispo Counties for tonight through early Wednesday. Blowing dust may also cause air quality to deteriorate at times. Winds could gust between 50 to 65 mph even in downtown Los Angeles, according to computer model guidance and the latest forecasts Monday evening.
“There will be an increased risk of fire ignitions due to downed trees and power lines, along with a threat of rapid fire spread and extreme fire behavior,” the Weather Service wrote.
Tyler Salas, a fire meteorologist with the U.S. Forest Service in Riverside, called the wind forecast a “slam dunk” but said other aspects of the forecast were challenging. For example, cooler weather, higher humidity and cloud cover could make it more difficult for fires to ignite and spread.
However, winds gusting between 60 and 80 mph are the overriding concern. Vegetation has been drying out since the last rainstorm in late December, and that drying accelerated during record warm, dry and windy weather over the past week.
“If anything really ignites, it’s going to take off in those winds,” Salas said.
High winds will also extend southward to the California border with Mexico and inland to Big Bear Lake and San Bernardino. Local topography will determine which areas see the highest gusts.
Damaging winds, elevated fire danger for Northern California
In Northern California, where winds began ramping up Sunday night, gusts exceeding 80 mph have already been reported and higher readings are possible as winds strengthen later today.
High wind warnings are in effect for the Sierra Nevada and the Bay Area, from the North Bay south to Monterey County.
“We expect damaging winds, mainly in higher elevations above 1,000 feet,” Duane Dykema, a meteorologist with the Weather Service’s Bay Area office, said in an interview.
However, gusty winds will also mix down into the more populated valleys.
The Weather Service recommends that people steer clear of trees and branches, and that they remain in the lower levels of their homes during the windstorm.
“Wind statistically is the second leading cause of death due to weather in our area,” the Bay Area office noted in a forecast discussion. “Too many people have lost their lives to falling trees.”
While wind damage will be the main impact in Northern California, fast-moving wildfires are not out of the question there either. In parts of the Bay Area, Sacramento Valley and Sierra foothills, dry grasses and shrubs remain despite intermittent rain this winter. The sustained dry winds could make it easier for fires to ignite and spread. Most of the region has been warmer and drier than average for many months, and it is also in severe to extreme drought.
“Even though we’re not putting out a fire weather watch for the Bay Area, there are still going to be issues with trees going down, and fire danger will be higher than normal for mid-January,” Dykema said.