Storm Prediction Center Day 2 Fire Weather Outlook
Created: Wed Dec 6 18:27:02 UTC 2017 ( | )
Click for Day 2 FireWX Areal Outline Product (KWNSPFWFD2)
ZCZC SPCFWDDY2 ALL FNUS22 KWNS 061826 Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1226 PM CST Wed Dec 06 2017 Valid 071200Z - 081200Z ...EXTREMELY CRITICAL FIRE WEATHER AREA FOR PORTIONS OF SOUTHERN CALIFORNIA... ...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF SOUTHERN CALIFORNIA... The ongoing forecast is on track and no changes are needed. See discussion below for forecast details. ..Leitman.. 12/06/2017 .PREV DISCUSSION... /ISSUED 0118 AM CST Wed Dec 06 2017/ ...Synopsis... Dangerous and extremely critical fire weather conditions are expected across a greater portion of southern CA on Day 2/Thursday compared to Day 1/Wednesday. Within large-scale upper troughing over much of the central/eastern CONUS, an embedded positively tilted upper trough will develop south-southeastward over the Rockies/Plains by 12Z Thursday. Enhanced north/northeasterly low- and mid-level flow around 30-40 kt on the western periphery of this upper trough will overspread the Southwest and southern CA Thursday morning and early afternoon. Highly amplified upper ridging will remain over the eastern Pacific and West Coast. At the surface, a broad area of high pressure over the northern Rockies and Great Basin will restrengthen late from Wednesday night into Thursday morning. A corresponding increase in offshore winds will occur across much of coastal southern CA through Thursday evening, supporting high-end critical to extremely critical fire weather conditions. ...Portions of Southern CA... Given the strengthening surface pressure gradient plus the enhanced low- and mid-level flow mentioned above, sustained northeasterly to easterly winds of 30-40 mph will likely occur across much of the higher terrain of southern CA from Thursday morning through at least the evening hours. This includes the mountains/foothills and adjacent areas of Ventura, Los Angeles, Orange, southwestern San Bernardino, western Riverside, and central/eastern San Diego counties. Stronger gusts of 50-70 mph will likely occur in favored higher terrain and passes where flow channeling will be maximized. RH values will easily fall/remain in the 5-10% range due to diurnal heating and low-level downslope warming/drying effects. Coupled with very dry/receptive fuels, these expected meteorological conditions support an extremely critical fire weather area. Large fire spread and extreme fire behavior will occur with any new/ongoing fires. Surrounding the extremely critical designation, critical fire weather conditions are anticipated. Here, sustained winds of 20-30 mph, with gusts to 40-50 mph, and RH values of 5-15% will be common. Both downtown Los Angeles and the LA basin along with San Diego have been included in a critical delineation. These dangerous fire weather conditions are forecast to continue through the entire Day 2/Thursday period, although the surface pressure gradient should relax slightly from late Thursday night into Friday morning. This should act to lessen winds somewhat across southern CA late in the period. ...Please see www.spc.noaa.gov/fire for graphic product...
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