NWS Storm Prediction Center - Day 1-2 Fire Weather Outlook
Updated: Mon Aug 20 16:16:03 UTC 2018
Aug 20, 2018 Day 1 Fire Weather Outlook
Day 1 Fire
 Population  Cities  CWAs  Interstates  Counties  FEMA Regions  Day 1 Surface Analysis 

Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
No Risk Areas Forecast
   FNUS21 KWNS 201615

   Day 1 Fire Weather Outlook  
   NWS Storm Prediction Center Norman OK
   1115 AM CDT Mon Aug 20 2018

   Valid 201700Z - 211200Z

   Minor spatial extensions to the elevated fire weather risk areas
   across Oregon and southern Idaho to account for latest model
   guidance, which depicts slightly stronger surface flow (amidst
   near-critical RH values) across these areas.  Additionally, a risk
   for isolated dry thunderstorms may also exist across western Utah
   and portions of the Salt Lake Valley.  The isolated dry thunderstorm
   risk area has been expanded northward to account for this risk.  

   Lastly, locally elevated fire weather conditions may also develop
   across portions of northwestern Washington State.  Local,
   terrain-related enhancements of surface wind will result in 10-15
   mph offshore flow amidst near-critical RH values (25-35%) and dry

   See the previous outlook for more details.

   ..Cook.. 08/20/2018

   .PREV DISCUSSION... /ISSUED 0148 AM CDT Mon Aug 20 2018/

   A positively-tilted upper-level trough and associated surface low
   will slowly deepen across the Pacific Northwest, into the northern
   Great Basin, with 40 knot northeasterly mid-level flow expected
   across parts of Washington into Oregon, and westerly 40-50 knot
   mid-level flow across the northern Great Basin into the Central
   Rockies. Ample mid-level moisture and deep-layer ascent will also be
   present across much of the Pacific Northwest into the northern Great
   Basin/northern Rockies regions to fuel at least isolated
   thunderstorms during the afternoon hours.

   ...Pacific Northwest...
   An elevated fire weather delineation was maintained across the
   Columbia Basin, as strong surface heating and associated deep
   boundary layer mixing will take place during the afternoon, allowing
   for stronger mid-level flow aloft to mix to the surface. 20-25% RH
   and 15-20 mph sustained northeasterly winds will be common.
   Elsewhere across the Pacific Northwest, an isolated dry thunderstorm
   delineation was maintained, as at least isolated thunderstorms, with
   a mix of wet and dry strikes, are expected to develop over areas
   where fuels are very receptive to fire spread. A few storms across
   eastern portions of the delineation may produce gusty and erratic
   winds, as some of these storms may lead to downward transport of
   stronger winds aloft.

   ...Portions of the Great Basin...
   Strong surface heating will allow the diurnal boundary layer to mix
   up to 500 mb during the late afternoon hours, allowing for stronger
   flow aloft to efficiently mix down to the surface. The net result
   will be sustained winds (southwesterly ahead of a cold front and
   northwesterly behind) in the 15-25 mph range through much of the
   afternoon, with critically low surface RH present. While an elevated
   delineation was extended for regions where available fuels were
   receptive to fire spread, some regions may easily experience at
   least locally critical conditions during the late afternoon hours,
   particularly out ahead of the cold front. 

   The latest convection allowing guidance also suggests that a cluster
   of isolated thunderstorms, with modest southwest to northeasterly
   movement, will develop later at night into early Tuesday morning in
   southwest Utah, towards the end of the forecast period. While a
   healthy mix of wet and dry strikes are expected with this activity,
   fuels are very receptive to fire spread in this area, hence the
   addition of an isolated dry thunderstorm delineation.

   ...Please see www.spc.noaa.gov/fire for graphic product...


   Source:  NWS Fire Weather Outlook
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