Storm Prediction Center Day 1 Fire Weather Outlook

Created: Thu Dec 7 07:43:03 UTC 2017 (20171207 1200Z Day 1 FireWX shapefile | 20171207 1200Z Day 1 FireWX KML)

Day 1 Fire Weather Forecast graphic
Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
Extreme 9,091 9,457,345 Santa Ana, CA...Anaheim, CA...Riverside, CA...Glendale, CA...San Bernardino, CA...
Critical 13,800 10,738,489 Los Angeles, CA...San Diego, CA...Long Beach, CA...Chula Vista, CA...Huntington Beach, CA...

Click for Day 1 FireWX Areal Outline Product

   FNUS21 KWNS 070742

   Day 1 Fire Weather Outlook  
   NWS Storm Prediction Center Norman OK
   0142 AM CST Thu Dec 07 2017

   Valid 071200Z - 081200Z


   Dangerous and extremely critical fire weather conditions are
   expected across a broad portion of southern CA today.

   Within large-scale upper troughing over much of the central/eastern
   CONUS, an embedded positively tilted upper trough will continue
   moving south-southeastward over the Rockies/Plains early this
   morning. Enhanced north/northeasterly low- and mid-level flow around
   30-40 kt on the western periphery of this upper trough has
   overspread the Southwest and southern CA, and these enhanced winds
   aloft will continue through at least the afternoon hours. Highly
   amplified upper ridging will remain over the eastern Pacific and
   parts of the West Coast.

   At the surface, a broad area of high pressure over the northern
   Rockies and Great Basin is in the process of restrengthening early
   this morning. A corresponding increase in offshore winds will occur
   across much of southern CA through this evening, supporting high-end
   critical to extremely critical fire weather conditions.

   ...Portions of Southern CA...
   The LAX-TPH pressure difference has strengthened to around -14 mb
   over the past several hours. Latest surface observations across
   southern CA show multiple locations in the mountains/foothills of
   Ventura and Los Angeles counties with sustained northerly to
   northeasterly winds of 30-35 mph, and gusts to 50-60 mph. RH values
   remain critically lowered in the 7-15% range for many areas.

   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 occur across much of the higher
   terrain of southern CA this morning through at least the evening
   hours. This includes the mountains/foothills and adjacent areas of
   far southeastern Santa Barbara, Ventura, Los Angeles, Orange,
   southwestern San Bernardino, western Riverside, and central/eastern
   San Diego counties. Stronger gusts of 50-80 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 this
   afternoon/evening due to diurnal heating and low-level downslope
   warming/drying effects. Coupled with very dry/receptive fuels, these
   expected meteorological conditions support the continuation of an
   extremely critical fire weather area with mainly small changes.
   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 across a broader portion of
   southern CA. 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 1/Thursday period,
   although the surface pressure gradient will likely relax slightly
   late tonight into Friday morning. This should act to lessen winds
   somewhat across southern CA late in the period.

   ...Portions of Southern AZ...
   A critical area has been included for portions of southern AZ where
   sustained winds of 20-30 mph will overlap with RH values lowered
   into the 5-15% range for a few hours this afternoon. Latest fuel
   guidance indicates fine fuels are now receptive to new fire starts.
   These critical fire weather conditions are expected to quickly
   diminish late this evening with the loss of diurnal heating and
   corresponding RH recovery.

   ..Gleason.. 12/07/2017

   ...Please see for graphic product...


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