Storm Prediction Center Day 1 Fire Weather Outlook
Created: Wed Dec 6 07:20:02 UTC 2017 ( | )
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ZCZC SPCFWDDY1 ALL FNUS21 KWNS 060718 Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0118 AM CST Wed Dec 06 2017 Valid 061200Z - 071200Z ...EXTREMELY CRITICAL FIRE WEATHER AREA FOR PORTIONS OF VENTURA AND LOS ANGELES COUNTIES FOR LATE TONIGHT IN SOUTHERN CALIFORNIA... ...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF SOUTHERN CALIFORNIA... ...Synopsis... Critical fire weather conditions will continue today and tonight across parts of southern CA as moderate to strong Santa Ana winds occur. Extremely critical conditions now appear likely across parts of Ventura and Los Angeles counties late tonight into early Thursday morning. These dangerous high-end critical to extremely critical conditions will continue into Day 2/Thursday. A highly amplified upper pattern will remain across the CONUS today as a large-scale upper trough/low encompasses the central/eastern CONUS. An upper ridge will be centered over the eastern Pacific and western CONUS. At the surface, a strong and broad area of high pressure will remain across the northern Rockies and Great Basin through the period. Generally cool post-frontal conditions will temper fire weather concerns east of the Rockies. ...Portions of Southern CA... The LAX-TPH surface pressure difference has averaged around -11.8 mb over the past few hours. Corresponding strong/gusty northeasterly to easterly winds of generally 20-30 mph continue per recent surface observations across much of the higher terrain of coastal southern CA. Higher gusts of 40-50 mph have been observed as well. A prolonged offshore wind event will continue across parts of southern CA today as the surface pressure gradient remains strong enough to support 20-30 mph northeasterly/easterly sustained winds. Gusts of 40-50 mph will likely continue across the mountains/foothills of coastal southern CA. RH values will remain critically lowered in the 5-15% range owing to both low-level downslope warming/drying and diurnal heating, with very poor to nonexistent overnight recovery. Latest deterministic and ensemble guidance indicates that the surface pressure gradient will be somewhat weaker through at least the first half of the Day 1/Wednesday period compared to yesterday. Still, high-end critical conditions will remain likely in favored higher terrain, and with very dry fuels in place, large fire spread will occur with any new/ongoing fires. Confidence has increased that the surface pressure gradient will restrengthen late tonight into early Thursday morning, and a corresponding increase in wind speeds/gusts will occur in this time frame. Both the 3 km NAM and experimental HRRR indicate sustained winds of 30-35 mph and sub-10% RH values will occur across portions of Ventura and Los Angeles counties for the last few hours of the Day 1/Wednesday period. Therefore, a small extremely critical area has been introduced to account for this threat. Extremely critical conditions are expected to become more widespread across coastal southern CA on Day 2/Thursday. See the Day 2 Fire Weather Outlook for more information. ..Gleason.. 12/06/2017 ...Please see www.spc.noaa.gov/fire for graphic product...
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