466  
FNUS22 KWNS 191945  
FWDDY2  
 
DAY 2 FIRE WEATHER OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK  
0244 PM CDT THU OCT 19 2017  
 
VALID 201200Z - 211200Z  
 
AN ELEVATED AREA HAS BEEN INTRODUCED FOR PARTS OF SOUTHERN CA,  
MAINLY FROM FRIDAY EVENING INTO THE EARLY MORNING HOURS ON SATURDAY.  
AS AN UPPER TROUGH MOVES EASTWARD ACROSS THE WESTERN CONUS ON DAY  
2/FRIDAY, A FAVORABLY ORIENTED SURFACE PRESSURE GRADIENT SHOULD  
PROMOTE STRONG/GUSTY NORTHERLY WINDS AROUND 15-25 MPH ACROSS THE  
SANTA YNEZ MOUNTAINS IN SANTA BARBARA COUNTY, AS WELL AS THE  
MOUNTAINS/FOOTHILLS OF VENTURA AND LOS ANGELES COUNTIES. WHILE RH  
VALUES MAY BECOME ONLY MARGINALLY REDUCED TO AROUND 15-20%,  
DOWNSLOPE WARMING/DRYING EFFECTS WILL LIKELY RESULT IN SOME ELEVATED  
FIRE WEATHER CONDITIONS ACROSS THIS REGION.  
 
THE ELEVATED AREA ACROSS PARTS OF EASTERN WY HAS BEEN EXPANDED  
NORTHWARD/EASTWARD/SOUTHWARD TO INCLUDE MORE OF THE NORTHERN AND  
CENTRAL HIGH PLAINS. CONFIDENCE REMAINS TOO LOW IN A SUFFICIENT  
OVERLAP OF CRITICALLY LOWERED RH VALUES AND 20+ MPH SUSTAINED WINDS  
TO JUSTIFY A CRITICAL AREA AT THIS TIME. SEE THE PREVIOUS DISCUSSION  
BELOW FOR MORE INFORMATION.  
 
..GLEASON.. 10/19/2017  
   
PREV DISCUSSION
 
/ISSUED 0254 AM CDT THU OCT 19 2017/  
   
..SYNOPSIS
 
 
A LARGE-SCALE TROUGH IS FORECAST TO MOVE FROM THE PACIFIC NORTHWEST  
INTO THE ROCKIES/HIGH PLAINS BY THE END OF DAY 2/FRIDAY. AS THIS  
OCCURS, A MID-LEVEL SPEED MAXIMUM WILL OVERSPREAD THE NORTHERN  
ROCKIES INTO THE NORTHERN HIGH PLAINS. ADDITIONALLY, LOW PRESSURE  
OVER ALBERTA/SASKATCHEWAN WILL MOVE EASTWARD TOWARD MANITOBA, WHILE  
A TRAILING COLD FRONT SHIFTS FROM THE GREAT BASIN TOWARD THE  
ROCKIES/HIGH PLAINS.  
   
..EASTERN WYOMING
 
 
STRONG/GUSTY SOUTHWESTERLY PRE-FRONTAL DOWNSLOPE SURFACE WINDS ARE  
FORECAST TO DEVELOP BY AFTERNOON, AS THE AFOREMENTIONED MID-LEVEL  
SPEED MAXIMUM NUDGES INTO THE AREA. A RELATIVELY DEEP MIXED LAYER  
WILL RESIDE BENEATH THE STRONGER FLOW, WHICH WILL PROMOTE EFFICIENT  
MIXING, WITH SUSTAINED SURFACE WIND IN EXCESS OF 20 MPH EXPECTED.  
DESPITE CRITICAL SURFACE WINDS, THE LATEST ENSEMBLE/DETERMINISTIC  
GUIDANCE CONTINUES TO SUGGEST THAT THE DEGREE OF LOW-LEVEL DRYING  
WILL BE LESS THAN PREVIOUS DAYS -- OWING IN PART TO INCREASING  
LOW-LEVEL MOISTURE. CURRENT INDICATIONS ARE THAT MINIMUM RH VALUES  
WILL REMAIN ABOVE CRITICAL THRESHOLDS (I.E., GREATER THAN 15%), WITH  
MINIMUM RH VALUES AROUND 15-25%. HOWEVER, GUIDANCE MAY NOT BE  
CAPTURING THE FULL EXTENT OF THE LOW-LEVEL WARMING/DRYING ASSOCIATED  
WITH THE DOWNSLOPE FLOW. THUS, WHILE A CRITICAL AREA WAS NOT  
INTRODUCED AT THIS TIME, ONE WOULD BE NEEDED IN FUTURE UPDATES IF  
TRENDS IN GUIDANCE SUGGEST GREATER LOW-LEVEL WARMING/DRYING.  
REGARDLESS, THE STRENGTH OF THE LOW-LEVEL WIND FIELD COUPLED WITH AT  
LEAST MODEST REDUCTIONS TO RH VALUES SUPPORTS MAINTAINING THE  
ONGOING ELEVATED FIRE WEATHER AREA (WITH ONLY MODEST ADJUSTMENTS).  
   
..PLEASE SEE WWW.SPC.NOAA.GOV/FIRE FOR GRAPHIC PRODUCT
 
 

 
 
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