642  
FNUS21 KWNS 060719  
FWDDY1  
 
DAY 1 FIRE WEATHER OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK  
0118 AM CST WED DEC 06 2017  
 
VALID 061200Z - 071200Z  
 
...EXTREMELY CRITICAL FIRE WEATHER AREA FOR PORTIONS OF VENTURA AND  
LOS ANGELES COUNTIES FOR LATE TONIGHT IN SOUTHERN CALIFORNIA...   
..CRITICAL FIRE WEATHER AREA FOR PORTIONS OF SOUTHERN CALIFORNIA
 
 
   
..SYNOPSIS
 
 
CRITICAL FIRE WEATHER CONDITIONS WILL CONTINUE TODAY AND TONIGHT  
ACROSS PARTS OF SOUTHERN CA AS MODERATE TO STRONG SANTA ANA WINDS  
OCCUR. EXTREMELY CRITICAL CONDITIONS NOW APPEAR LIKELY ACROSS PARTS  
OF VENTURA AND LOS ANGELES COUNTIES LATE TONIGHT INTO EARLY THURSDAY  
MORNING. THESE DANGEROUS HIGH-END CRITICAL TO EXTREMELY CRITICAL  
CONDITIONS WILL CONTINUE INTO DAY 2/THURSDAY.  
 
A HIGHLY AMPLIFIED UPPER PATTERN WILL REMAIN ACROSS THE CONUS TODAY  
AS A LARGE-SCALE UPPER TROUGH/LOW ENCOMPASSES THE CENTRAL/EASTERN  
CONUS. AN UPPER RIDGE WILL BE CENTERED OVER THE EASTERN PACIFIC AND  
WESTERN CONUS. AT THE SURFACE, A STRONG AND BROAD AREA OF HIGH  
PRESSURE WILL REMAIN ACROSS THE NORTHERN ROCKIES AND GREAT BASIN  
THROUGH THE PERIOD. GENERALLY COOL POST-FRONTAL CONDITIONS WILL  
TEMPER FIRE WEATHER CONCERNS EAST OF THE ROCKIES.  
   
..PORTIONS OF SOUTHERN CA
 
 
THE LAX-TPH SURFACE PRESSURE DIFFERENCE HAS AVERAGED AROUND -11.8 MB  
OVER THE PAST FEW HOURS. CORRESPONDING STRONG/GUSTY NORTHEASTERLY TO  
EASTERLY WINDS OF GENERALLY 20-30 MPH CONTINUE PER RECENT SURFACE  
OBSERVATIONS ACROSS MUCH OF THE HIGHER TERRAIN OF COASTAL SOUTHERN  
CA. HIGHER GUSTS OF 40-50 MPH HAVE BEEN OBSERVED AS WELL.  
 
A PROLONGED OFFSHORE WIND EVENT WILL CONTINUE ACROSS PARTS OF  
SOUTHERN CA TODAY AS THE SURFACE PRESSURE GRADIENT REMAINS STRONG  
ENOUGH TO SUPPORT 20-30 MPH NORTHEASTERLY/EASTERLY SUSTAINED WINDS.  
GUSTS OF 40-50 MPH WILL LIKELY CONTINUE ACROSS THE  
MOUNTAINS/FOOTHILLS OF COASTAL SOUTHERN CA. RH VALUES WILL REMAIN  
CRITICALLY LOWERED IN THE 5-15% RANGE OWING TO BOTH LOW-LEVEL  
DOWNSLOPE WARMING/DRYING AND DIURNAL HEATING, WITH VERY POOR TO  
NONEXISTENT OVERNIGHT RECOVERY. LATEST DETERMINISTIC AND ENSEMBLE  
GUIDANCE INDICATES THAT THE SURFACE PRESSURE GRADIENT WILL BE  
SOMEWHAT WEAKER THROUGH AT LEAST THE FIRST HALF OF THE DAY  
1/WEDNESDAY PERIOD COMPARED TO YESTERDAY. STILL, HIGH-END CRITICAL  
CONDITIONS WILL REMAIN LIKELY IN FAVORED HIGHER TERRAIN, AND WITH  
VERY DRY FUELS IN PLACE, LARGE FIRE SPREAD WILL OCCUR WITH ANY  
NEW/ONGOING FIRES.  
 
CONFIDENCE HAS INCREASED THAT THE SURFACE PRESSURE GRADIENT WILL  
RESTRENGTHEN LATE TONIGHT INTO EARLY THURSDAY MORNING, AND A  
CORRESPONDING INCREASE IN WIND SPEEDS/GUSTS WILL OCCUR IN THIS TIME  
FRAME. BOTH THE 3 KM NAM AND EXPERIMENTAL HRRR INDICATE SUSTAINED  
WINDS OF 30-35 MPH AND SUB-10% RH VALUES WILL OCCUR ACROSS PORTIONS  
OF VENTURA AND LOS ANGELES COUNTIES FOR THE LAST FEW HOURS OF THE  
DAY 1/WEDNESDAY PERIOD. THEREFORE, A SMALL EXTREMELY CRITICAL AREA  
HAS BEEN INTRODUCED TO ACCOUNT FOR THIS THREAT. EXTREMELY CRITICAL  
CONDITIONS ARE EXPECTED TO BECOME MORE WIDESPREAD ACROSS COASTAL  
SOUTHERN CA ON DAY 2/THURSDAY. SEE THE DAY 2 FIRE WEATHER OUTLOOK  
FOR MORE INFORMATION.  
 
..GLEASON.. 12/06/2017  
   
..PLEASE SEE WWW.SPC.NOAA.GOV/FIRE FOR GRAPHIC PRODUCT
 
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab SPC Page Main Text Page