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LASD - Altadena Station, Los Angeles County Sheriff
Tuesday August 21st, 2012 :: 04:11 p.m. PDT


Red Flag Warning in Effect for Los Angeles County Mountains

NWS Los Angeles/Oxnard Weather Briefing for Red Flag Warning August 21-22, 2012

***Red Flag Warning in Effect for Santa Barbara, Ventura, and Los Angeles County Mountains, Valleys, and Deserts Tonight Through Wednesday Afternoon***

SYNOPSIS: A weak low pressure system will develop off the central California coast Tuesday evening then move slowly across the region Tuesday night and Wednesday. The atmosphere will become more unstable as the low approaches but the moisture source will be very limited. This scenario will bring a potential for dry lightning, or thunderstorms that contain little or no rainfall, across much of southwest California from about the San Luis Obispo County Mountains south and east across most of Ventura and Los Angeles Counties. Fire weather concerns are high given the very dry fuel conditions and recent above normal temperatures.

IMPACTS: Dry lightning could result in fire ignitions and gusty outflow winds from collapsing thunderstorms would help spread fire rapidly. The recent heat wave has primed dry vegetation across the entire region with most areas reporting critical fuel moisture levels. Boaters should be aware that thunderstorms could bring dangerous lightning, shifting winds, and choppy seas.

TIMING: The main dry lightning threat will develop after midnight with thunderstorms likely to form over the coastal waters then move inland overnight and early Wednesday morning. Storm movement will generally be from southwest to northeast. Thunderstorms will likely shift to the mountains and deserts and away from the coast and valley areas by midday Wednesday, continuing through Wednesday afternoon. All storm activity should wind down by early Wednesday evening.

FORECAST CONFIDENCE: High confidence for dry lightning to develop across the region tonight and Wednesday, but low confidence for the overall amount of thunderstorm activity.

Updates and statements about this thunderstorm event can be accessed on our web site at
The latest Red Flag Warning can be accessed at

Attached is our current Weather Story graphic.

Eric Boldt
Warning Coordination Meteorologist
National Weather Service Los Angeles/Oxnard
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LASD - Altadena Station, Los Angeles County Sheriff
780 E Altadena Dr
Altadena, CA 91001

Emergency: 9-1-1
Non-emergencies: 626-798-1131

Altadena Sheriff Station

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