102  
FNUS21 KWNS 050736  
FWDDY1  
 
DAY 1 FIRE WEATHER OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK  
0135 AM CST TUE DEC 05 2017  
 
VALID 051200Z - 061200Z  
 
...EXTREMELY CRITICAL FIRE WEATHER AREA FOR PORTIONS OF  
VENTURA...LOS ANGELES...ORANGE...SAN BERNARDINO...AND RIVERSIDE  
COUNTIES IN SOUTHERN CALIFORNIA...   
..CRITICAL FIRE WEATHER AREA FOR PORTIONS OF SOUTHERN CALIFORNIA
 
 
   
..SYNOPSIS
 
 
A LARGE-SCALE UPPER TROUGH OVER THE CENTRAL/EASTERN CONUS AND  
ONTARIO WILL MAKE ONLY SLOW EASTWARD PROGRESS TODAY. MEANWHILE,  
UPPER RIDGING OVER THE EASTERN PACIFIC WILL BECOME PROMINENT ACROSS  
PARTS OF THE WESTERN CONUS BY LATE TONIGHT. AT THE SURFACE, A BROAD  
AREA OF STRONG HIGH PRESSURE WILL REMAIN ACROSS THE NORTHERN ROCKIES  
AND GREAT BASIN, SUPPORTING A STRONG OFFSHORE SANTA ANA WIND EVENT  
ACROSS PARTS OF SOUTHERN CA THROUGH THE PERIOD. FARTHER EAST, A COLD  
FRONT WILL CONTINUE EASTWARD/SOUTHEASTWARD ACROSS THE OH/TN VALLEYS  
AND SOUTHEAST, WITH GUSTY POST-FRONTAL WINDS OCCURRING ACROSS PARTS  
OF THE PLAINS.  
   
..PORTIONS OF SOUTHERN CA
 
 
AVERAGE PRESSURE DIFFERENCE EARLY THIS MORNING (02-06Z) FOR LAX-TPH  
IS AROUND -14 MB, AND LAX-DAG DIFFERENCE IS ABOUT -6.5 MB. THE  
PRESSURE GRADIENT SHOULD STRENGTHEN FURTHER THROUGH 12-16Z ACROSS  
SOUTHERN CA, SUPPORTING AN INCREASE IN ALREADY VERY STRONG/GUSTY  
SURFACE WINDS OCCURRING ACROSS THE HIGHER TERRAIN OF THIS REGION.  
SURFACE OBSERVATIONS OVER THE PAST FEW HOURS (03-06Z) ACROSS  
SOUTHERN CA SHOW NUMEROUS LOCATIONS WITH SUSTAINED WINDS OF 20-40  
MPH, AND RH VALUES OF 9-15%. MULTIPLE SITES IN HIGHER TERRAIN HAVE  
REPORTED WIND GUSTS OF 50-70 MPH.  
 
AN EXTREMELY CRITICAL FIRE WEATHER AREA IS IN PLACE FOR PARTS OF  
VENTURA, LOS ANGELES, ORANGE, SAN BERNARDINO, AND RIVERSIDE COUNTIES  
IN SOUTHERN CA FOR TODAY. THIS IS A CONTINUATION AND EXPANSION OF  
THE EXTREMELY CRITICAL AREA THAT WAS VALID YESTERDAY (MONDAY).  
ACROSS THESE AREAS, SUSTAINED WINDS OF 30-40 MPH WILL CONTINUE  
THROUGH AT LEAST THIS EVENING WHILE THE SURFACE PRESSURE GRADIENT IS  
MAXIMIZED. STRONGER GUSTS OF 60-80 MPH WILL LIKELY OCCUR IN THE  
HIGHER TERRAIN OF THESE COUNTIES GIVEN ENHANCED NORTHEASTERLY  
LOW-LEVEL FLOW THAT WILL REMAIN PRESENT. THESE VERY STRONG DOWNSLOPE  
WINDS WILL ACT TO WARM/DRY THE LOW LEVELS, AND COUPLED WITH DIURNAL  
HEATING, RH VALUES WILL LIKELY FALL INTO THE 4-10% RANGE FOR MUCH OF  
THE DAY. FUELS WILL ALSO REMAIN VERY DRY AND RECEPTIVE TO LARGE FIRE  
STARTS AND EXTREME FIRE SPREAD GIVEN THE EXPECTED/ONGOING  
METEOROLOGICAL CONDITIONS.  
 
OF NOTE, DOWNTOWN LOS ANGELES AND MUCH OF THE LA BASIN HAVE BEEN  
SPECIFICALLY EXCLUDED FROM THE EXTREMELY CRITICAL AREA, AS SUSTAINED  
WINDS WILL LIKELY REMAIN SOMEWHAT LESS (GENERALLY IN THE 20-30 MPH  
RANGE) PER CONSENSUS OF LATEST HIGH-RESOLUTION GUIDANCE. REGARDLESS,  
CRITICAL CONDITIONS ARE STILL EXPECTED FOR THIS MAJOR METRO AREA AND  
VICINITY.  
 
CRITICAL FIRE WEATHER CONDITIONS WILL OCCUR ACROSS A LARGER PORTION  
OF SOUTHERN CA SURROUNDING THE EXTREMELY CRITICAL AREA. HERE,  
SUSTAINED WINDS OF 20-30 MPH WILL BE COMMON, WITH GUSTS OF 45-60 MPH  
LIKELY IN THE MOUNTAINS/FOOTHILLS. RH VALUES OF 5-15% WILL ALSO  
OCCUR THROUGH THE PERIOD DUE TO CONTINUED DOWNSLOPE WARMING/DRYING  
OF AN ALREADY DRY AIRMASS. RH RECOVERY LATE TONIGHT INTO WEDNESDAY  
MORNING WILL LIKELY BE VERY POOR AS WINDS WILL REMAIN STRONG/GUSTY  
ACROSS MUCH OF SOUTHERN CA. CONSENSUS OF LATEST GUIDANCE INDICATES  
THE PRESSURE GRADIENT ACROSS THIS REGION WILL WEAKEN SOMEWHAT  
TONIGHT INTO EARLY WEDNESDAY MORNING, AND WIND SPEEDS/GUSTS MAY  
LESSEN SLIGHTLY AS A RESULT. HOWEVER, CRITICAL FIRE WEATHER  
CONDITIONS WILL LIKELY PERSIST ACROSS BOTH THE CRITICAL AND  
EXTREMELY CRITICAL DESIGNATIONS THROUGH EARLY WEDNESDAY MORNING (END  
OF THE DAY 1/TUESDAY PERIOD AND CONTINUING INTO DAY 2/WEDNESDAY).  
   
..PORTIONS OF THE CENTRAL PLAINS TO LOWER MO VALLEY
 
 
ALTHOUGH TEMPERATURES ARE FORECAST TO REMAIN COOL ACROSS PARTS OF  
THE CENTRAL PLAINS INTO THE LOWER MO VALLEY, GENERALLY IN THE MID  
40S TO LOWER 50S, STRONG/GUSTY POST-FRONTAL WINDS AROUND 15-20 MPH  
ARE EXPECTED TO DEVELOP AS ENHANCED MID-LEVEL WINDS BECOME MIXED TO  
THE SURFACE. WITH A DRY POST-FRONTAL AIRMASS IN PLACE ACROSS THIS  
REGION, RH VALUES SHOULD BECOME LOWERED INTO THE 20-25% RANGE FOR A  
FEW HOURS THIS AFTERNOON, SUPPORTING ELEVATED FIRE WEATHER  
CONDITIONS WHERE FUELS ARE DRY/DORMANT.  
 
..GLEASON.. 12/05/2017  
   
..PLEASE SEE WWW.SPC.NOAA.GOV/FIRE FOR GRAPHIC PRODUCT
 
 

 
 
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