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Extreme Santa Ana wind event predicted in California

By Alex Sosnowski, Accuweather.com

Gusty winds and almost summerlike warmth created dangerous conditions and elevated the fire danger to critical levels across parts of Southern California on Thursday evening into Friday.

Some communities already faced evacuations as a fire broke out and winds quickly fanned the flames in Ventura County. AccuWeather meteorologists say that residents should remain prepared to evacuate on short notice as dangerous fire weather is far from over.

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The setup already began to whip up fires Thursday evening. The Erbes Fire ignited in Thousand Oaks around 5 p.m., prompting evacuation orders in the area. Within 2 hours, the fire had consumed 250 acres, and the blaze threatened structures as firefighters worked to contain the perimeter and extinguish hot spots. Containment was at 90% as of Friday morning, the Ventura County sheriff's office said.

Elevated and critical fire conditions will continue in Southern California through this weekend as rounds of strong northeasterly winds will kick up, and AccuWeather forecasters are sounding the alarm that an even more intense wind event could exacerbate conditions and rapidly spread fires early in the week.

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Red flag warnings were posted for parts of Southern California, and the National Weather Service warned that conditions will be "favorable for extreme fire behavior which would threaten life and property" and added that people should use "extreme caution" with any sources that could lead to fire ignition. Parking cars over dry brush, for instance, or using open flames and outdoor grills could spark fires.

"The setup for Monday to Tuesday checks a lot of boxes for a strong Santa Ana wind event with gusts in the neighborhood of 80-100 mph in most northeast wind-prone locations of Southern California," AccuWeather senior meteorologist Dave Samuhel said.

Utility companies may be forced to cut power as a precaution to avoid downed live wires sparking blazes. Winds are forecast to be strong enough to topple trees, break tree limbs and knock down power lines.

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The high wind event will be fueled by the usual difference in atmospheric pressure as an area of high pressure will build over the Northwest and Great Basin regions. Air will then be forced over the tops of the mountains and through the passes and canyons of California, which can increase local wind gusts further.

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There will be a boost in winds from a pattern high in the atmosphere as well. A strong jet stream disturbance is forecast to drop southward along the Pacific Coast states.

"The combination of the high pressure area, the jet stream disturbance and a developing storm near the coast of the northern part of Baja California, Mexico, will really get the wind cranking," AccuWeather meteorologist Brandon Buckingham said.

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"The circulation around the high pressure and storm (low pressure) will create moderate winds, but the upper-level disturbance will give the winds a big boost, especially where winds at the surface roughly align from the same direction as the winds aloft," Buckingham explained.

Even though the strongest winds will tend to focus over much of coastal Southern California and areas just inland of the coast, the wind event will be a regional one where gusts can kick up dust, create difficult handling of vehicles in open areas and raise the potential for spotty fires throughout the dry landscape of the Southwest.

"In Northern California, the area from San Francisco to the Sierra Nevada foothills can expect some strong winds as well early next week," Samuhel said.

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Unlike the weather pattern that created moderate Santa Ana winds and a surge in temperature this week, the upcoming event will be associated with progressively cooler air.

The southward plunge in the jet stream in the Southwestern states will allow colder air that will build up over western Canada and the interior Northwest and then move southward.

"The combination of the jet stream disturbance and the storm forecast to develop over the northwestern part of Mexico or just offshore will also begin to pump some moisture into the southwestern U.S.," Buckingham said. "By next Tuesday, some desert rain and mountain snow are foreseen over the interior Southwest and in northern Mexico."

Forecasters say there are some questions as to how much rain and mountain snow will develop in Southern California with this storm, however.

There is the chance for some showers to pop up Tuesday to Wednesday in parts of Southern California, but this particular storm may set up so far south that rain may struggle to reach the area, at least initially.

Even if rain fails to arrive and ease fire concerns by the middle of next week, there is some hope of relief from fire and drought concerns prior to next week's end. The first storm is likely to signify a change in the weather pattern for the Southwest and the western U.S. in general.

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"This storm system may only be the first in a series of storm systems next week that may try to bring along much-needed rain and mountain snow to Southern California and the Southwest," Buckingham said.

Despite much of Southern California being doused by heavy rain ranging from 0.50 of an inch to 2 inches during late December, it has not rained since then. Even though that rain helped to soak vegetation, the brush has since dried out to the point where it has once again become tinder dry and fuel for any sparks or small fires that develop. The late-December rain did not put a dent in drought conditions either. A moderate to exceptional drought is gripping a large portion of the Southwest, according to the United States Drought Monitor.

Early indications are that the upcoming pattern may allow a storm to drop southward along the West Coast every three to four days or so through the end of January.

The same pattern may also continue to bring some wind events and fire risk in between the storms, but the cumulative effect might be to really knock down the fire potential and get some moisture in the ground and flowing through streams in the region that could prove beneficial in the long run.

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Regardless of how stormy the pattern becomes or not, much cooler conditions are in store for coastal areas of the West, and much colder conditions are predicted across the interior, relative to most of the winter thus far.

Temperatures over the Southwest for the latter third of January may average a few degrees Fahrenheit below normal along the coast to as much as 10 degrees below normal over parts of the interior. The normal high for Downtown Los Angeles on Jan. 25 is 68, and the normal high in Flagstaff, Ariz., is 43.

The pattern change could bring quite the shock to people who live across the region, especially following almost summerlike temperatures that are forecast to average 10-20 degrees above normal this weekend.

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