128  
FNUS21 KWNS 070742  
FWDDY1  
 
DAY 1 FIRE WEATHER OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK  
0142 AM CST THU DEC 07 2017  
 
VALID 071200Z - 081200Z  
 
...EXTREMELY CRITICAL FIRE WEATHER AREA FOR PORTIONS OF SOUTHERN  
CALIFORNIA...   
..CRITICAL FIRE WEATHER AREA FOR PORTIONS OF SOUTHERN CALIFORNIA
 
   
..CRITICAL FIRE WEATHER AREA FOR PORTIONS OF SOUTHERN ARIZONA
 
 
   
..SYNOPSIS
 
 
DANGEROUS AND EXTREMELY CRITICAL FIRE WEATHER CONDITIONS ARE  
EXPECTED ACROSS A BROAD PORTION OF SOUTHERN CA TODAY.  
 
WITHIN LARGE-SCALE UPPER TROUGHING OVER MUCH OF THE CENTRAL/EASTERN  
CONUS, AN EMBEDDED POSITIVELY TILTED UPPER TROUGH WILL CONTINUE  
MOVING SOUTH-SOUTHEASTWARD OVER THE ROCKIES/PLAINS EARLY THIS  
MORNING. ENHANCED NORTH/NORTHEASTERLY LOW- AND MID-LEVEL FLOW AROUND  
30-40 KT ON THE WESTERN PERIPHERY OF THIS UPPER TROUGH HAS  
OVERSPREAD THE SOUTHWEST AND SOUTHERN CA, AND THESE ENHANCED WINDS  
ALOFT WILL CONTINUE THROUGH AT LEAST THE AFTERNOON HOURS. HIGHLY  
AMPLIFIED UPPER RIDGING WILL REMAIN OVER THE EASTERN PACIFIC AND  
PARTS OF THE WEST COAST.  
 
AT THE SURFACE, A BROAD AREA OF HIGH PRESSURE OVER THE NORTHERN  
ROCKIES AND GREAT BASIN IS IN THE PROCESS OF RESTRENGTHENING EARLY  
THIS MORNING. A CORRESPONDING INCREASE IN OFFSHORE WINDS WILL OCCUR  
ACROSS MUCH OF SOUTHERN CA THROUGH THIS EVENING, SUPPORTING HIGH-END  
CRITICAL TO EXTREMELY CRITICAL FIRE WEATHER CONDITIONS.  
   
..PORTIONS OF SOUTHERN CA
 
 
THE LAX-TPH PRESSURE DIFFERENCE HAS STRENGTHENED TO AROUND -14 MB  
OVER THE PAST SEVERAL HOURS. LATEST SURFACE OBSERVATIONS ACROSS  
SOUTHERN CA SHOW MULTIPLE LOCATIONS IN THE MOUNTAINS/FOOTHILLS OF  
VENTURA AND LOS ANGELES COUNTIES WITH SUSTAINED NORTHERLY TO  
NORTHEASTERLY WINDS OF 30-35 MPH, AND GUSTS TO 50-60 MPH. RH VALUES  
REMAIN CRITICALLY LOWERED IN THE 7-15% RANGE FOR MANY AREAS.  
 
GIVEN THE STRENGTHENING SURFACE PRESSURE GRADIENT PLUS THE ENHANCED  
LOW- AND MID-LEVEL FLOW MENTIONED ABOVE, SUSTAINED NORTHEASTERLY TO  
EASTERLY WINDS OF 30-40 MPH WILL OCCUR ACROSS MUCH OF THE HIGHER  
TERRAIN OF SOUTHERN CA THIS MORNING THROUGH AT LEAST THE EVENING  
HOURS. THIS INCLUDES THE MOUNTAINS/FOOTHILLS AND ADJACENT AREAS OF  
FAR SOUTHEASTERN SANTA BARBARA, VENTURA, LOS ANGELES, ORANGE,  
SOUTHWESTERN SAN BERNARDINO, WESTERN RIVERSIDE, AND CENTRAL/EASTERN  
SAN DIEGO COUNTIES. STRONGER GUSTS OF 50-80 MPH WILL LIKELY OCCUR IN  
FAVORED HIGHER TERRAIN AND PASSES WHERE FLOW CHANNELING WILL BE  
MAXIMIZED. RH VALUES WILL EASILY FALL/REMAIN IN THE 5-10% RANGE THIS  
AFTERNOON/EVENING DUE TO DIURNAL HEATING AND LOW-LEVEL DOWNSLOPE  
WARMING/DRYING EFFECTS. COUPLED WITH VERY DRY/RECEPTIVE FUELS, THESE  
EXPECTED METEOROLOGICAL CONDITIONS SUPPORT THE CONTINUATION OF AN  
EXTREMELY CRITICAL FIRE WEATHER AREA WITH MAINLY SMALL CHANGES.  
LARGE FIRE SPREAD AND EXTREME FIRE BEHAVIOR WILL OCCUR WITH ANY  
NEW/ONGOING FIRES.  
 
SURROUNDING THE EXTREMELY CRITICAL DESIGNATION, CRITICAL FIRE  
WEATHER CONDITIONS ARE ANTICIPATED ACROSS A BROADER PORTION OF  
SOUTHERN CA. HERE, SUSTAINED WINDS OF 20-30 MPH, WITH GUSTS TO 40-50  
MPH, AND RH VALUES OF 5-15% WILL BE COMMON. BOTH DOWNTOWN LOS  
ANGELES AND THE LA BASIN ALONG WITH SAN DIEGO HAVE BEEN INCLUDED IN  
A CRITICAL DELINEATION. THESE DANGEROUS FIRE WEATHER CONDITIONS ARE  
FORECAST TO CONTINUE THROUGH THE ENTIRE DAY 1/THURSDAY PERIOD,  
ALTHOUGH THE SURFACE PRESSURE GRADIENT WILL LIKELY RELAX SLIGHTLY  
LATE TONIGHT INTO FRIDAY MORNING. THIS SHOULD ACT TO LESSEN WINDS  
SOMEWHAT ACROSS SOUTHERN CA LATE IN THE PERIOD.  
   
..PORTIONS OF SOUTHERN AZ
 
 
A CRITICAL AREA HAS BEEN INCLUDED FOR PORTIONS OF SOUTHERN AZ WHERE  
SUSTAINED WINDS OF 20-30 MPH WILL OVERLAP WITH RH VALUES LOWERED  
INTO THE 5-15% RANGE FOR A FEW HOURS THIS AFTERNOON. LATEST FUEL  
GUIDANCE INDICATES FINE FUELS ARE NOW RECEPTIVE TO NEW FIRE STARTS.  
THESE CRITICAL FIRE WEATHER CONDITIONS ARE EXPECTED TO QUICKLY  
DIMINISH LATE THIS EVENING WITH THE LOSS OF DIURNAL HEATING AND  
CORRESPONDING RH RECOVERY.  
 
..GLEASON.. 12/07/2017  
   
..PLEASE SEE WWW.SPC.NOAA.GOV/FIRE FOR GRAPHIC PRODUCT
 
 

 
 
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