799  
FNUS21 KWNS 201616  
FWDDY1  
 
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  
FUELS.  
 
SEE THE PREVIOUS OUTLOOK FOR MORE DETAILS.  
 
..COOK.. 08/20/2018  
   
PREV DISCUSSION
 
/ISSUED 0148 AM CDT MON AUG 20 2018/  
   
..SYNOPSIS
 
 
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
 
 

 
 
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