AccuWeather forecasters are warning residents and visitors in Southern California to brace for a strong Santa Ana event that will not only substantially raise the risk of wildfires but can also trigger power outages and may lead to property damage during the second half of this week.
Atmospheric pressure is expected to build across the interior western United States, and a strong jet stream will bend southward over the Southwestern states and northern Mexico, setting the stage for a round of strong northeasterly winds in Southern California, known as Santa Ana winds.
"A very strong area of high pressure is forecast to build southward through the Rockies and Great Basin later this week," according to AccuWeather Senior Meteorologist Heather Zehr.
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This setup will create a flow of air from the interior West to the Pacific Ocean around Southern California. As the air flows through the canyons and passes, it will accelerate and gain even more speed blowing downhill from the mountains due to the effects of gravity.
Meanwhile, the presence of a strong jet stream overhead may add another layer of intensity to the winds in this case.
Should the wind direction line up both near the ground and high in the atmosphere, some very powerful gusts aloft can be stirred down to the surface.
Winds will increase during Wednesday night from the breezy levels on Wednesday. Peak winds and the strongest gusts are expected to develop on Thursday into Friday.
AccuWeather meteorologists are concerned for gusts frequenting 40-60 mph through the northeast-southwest orientated passes to coastal areas and even the waters and islands offshore. "There is the potential for a few gusts near 90 mph in some of the windiest spots with this strong Santa Ana event," Brett Anderson, AccuWeather senior meteorologist, said.
"If the winds fail to line up near the ground and aloft and the core of high pressure settles farther inland over the West, a more moderate, rather than strong Santa Ana event can occur," Senior AccuWeather Meteorologist Dave Houk explained.
"But, should a less-severe Santa Ana case unfold, there will still be problems due to wind and fire danger," Houk stated.
Wind gusts frequenting 40-60 mph with peak gusts near 90 mph will be strong enough to break large tree limbs, knock over trees and flip over trucks and campers. The high winds are likely to lead to power outages at a local and regional level. Sparks generated by downed power lines will threaten to initiate fires that can quickly escalate into major and fast-moving wildfires.
Even though this Santa Ana event will not be accompanied by surging temperatures but rather cool conditions, humidity levels will be quite low. Highs in Downtown Los Angeles, which will generally be spared by the high winds, are forecast to be in the lower 70s F each day this week close or just above the normal high of 69 in early December.
Despite much of Southern California not being in an official drought, according to the United States Drought Monitor, ongoing dry air will result in extremely dry brush.
"Because the air will be very dry, the strong winds and ongoing dry landscape will combine to create a critical fire risk from Thursday through Friday," Zehr said. Relative humidity levels can crash into the teens and even the single digits at times during the daylight hours as the winds roar.
The Los Angeles National Weather Service tweeted that red flag conditions are likely from Wednesday night through Friday, noting that the winds will create "extreme behavior" of any fires that ignite. Fire weather watches were issued across parts of Southern California. The NWS shared a video on precautionary steps people can take to protect their homes from wildfires.
Forecasters urged people to avoid the use of open flames and outdoor power equipment and avoid parking vehicles over dry brush later this week.
Just last week, a moderate to strong Santa Ana event brought gusts close to 80 mph over the San Gabriel and Santa Ana mountains on Thanksgiving Day and last Friday. Tens of thousands of utility customers in Southern California had their power turned off around the Thanksgiving holiday as a precaution, according to the Associated Press.
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