- Sunday September 29th, 2013 :: 06:21 p.m. PDT
Very warm and dry conditions will bring elevated fire danger to LA County Thurs-Sat. Single digit humidity
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From the National Weather Service:
Very warm and dry conditions will bring elevated fire danger to So Cal. Single digit humidity readings observed.
On Thursday (10/03/13), a strong upper level trough of low pressure will move southward into the Great Basin as an upper ridge builds off the West Coast. Dry northerly winds will begin to impact San Luis Obispo and Santa Barbara Counties Thursday afternoon and evening.
As the surface high builds into Nevada, the flow will shift to northeast and begin to affect Ventura and Los Angeles Counties late Thursday night (10/03/13) into early Friday (10/04/13).
These gusty Santa Ana winds are expected to persist through Saturday (10/05/13), bringing an extended period of warm, very dry and windy conditions to much of Southwest California.
Critical fire weather conditions will be possible during this time period as the hot, dry and windy conditions interact with very dry fuels in place across the area.
The greatest fire weather threat will likely be across Ventura and Los Angeles Counties.
Residents of Southwest California are urged to stay tuned to the latest National Weather Service statements and warnings on this developing weather situation:
National Weather Service:
NWS Update...Potential for Critical Fire Weather Conditions starting Late Thursday, 10/03/13
...Dry and Warm Offshore Wind Event Possible Thursday Evening Through Saturday...
Large Fire Growth Potential - the combination of very low relative humidity and gusty offshore winds may bring a significant threat of critical fire weather to southern California Thursday evening through Saturday. Extremely dry fuel conditions already in place would allow for rapid fire growth potential if winds and dry air develop as projected late in the week. The air mass will warm considerably as air is forced down the mountain slopes toward the beaches on Friday and Saturday, adding to the fire growth potential in Ventura and Los Angeles Counties.
Winds will begin to turn increasingly onshore on Sunday, resulting in slightly cooler temperatures and higher humidities. However, there may continue to be several hours of critical fire weather conditions during this transitional period on Sunday.
A large low pressure system will move across the Pacific Northwest on Wednesday and into the central Rockies by Thursday. This "inside slider" will likely bring increasing offshore winds to southern California late Thursday through Saturday. North winds (Sundowner winds) will first develop across the Santa Ynez Mountains of Santa Barbara County Thursday afternoon into Thursday night. Then, northeast winds (Santa Ana winds) will develop across the Ventura and Los Angeles County by early Friday morning, continuing into Saturday. Very dry air is likely to accompany the onset of the gusty winds with many areas experiencing relative humidity less than 10 percent on Friday and Saturday. In addition, temperatures on these days will rise above normal from the foothills to the beaches of Ventura and Los Angeles Counties. At this time, winds are expected to weaken and turn back onshore on Sunday, which would also lead to slightly cooler temperatures and slowly increasing humidity.
TIMING AND FORECAST CONFIDENCE
Although this event is 4-5 days from today, there has been a trend of consistent computer model data to give us moderate confidence of the potential impacts and timing. The details on the overall strength and duration of the winds on Friday and Saturday are less certain at this time. However, this event looks drier and windier than what occurred last week.
Please stay alert to additional emails and/or NWS Los Angeles forecasts this week as this system approaches and as more detailed information becomes available.
NWS will continue to provide email updates if the forecast changes or check our website at www.weather.gov/losangeles
Santa Barbara County Office of Emergency Management
Captain Mike Parker
Sheriff's Headquarters Bureau - Newsroom
Los Angeles County Sheriff's Department
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