654  
FXUS02 KWBC 081600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1100 AM EST FRI DEC 08 2017  
 
VALID 12Z MON DEC 11 2017 - 12Z FRI DEC 15 2017  
 
...A MIDWEST/GREAT LAKES THROUGH NORTHEASTERN U.S. HEAVY SNOW  
THREAT...  
 
   
..PATTERN OVERVIEW/PREDICTABILITY ASSESSMENT/PREFERENCES
 
 
THE SYNOPTIC-SCALE PATTERN IS HIGHLIGHTED BY A MEAN UPPER TROUGH  
EAST OF THE PLAINS. MULTIPLE EMBEDDED SHORTWAVES ROTATE WITHIN THE  
DEEP CYCLONIC FLOW FOSTER DEVELOPMENT OF SEVERAL SURFACE WAVES.  
500MB HEIGHT ANOMALIES ARE IN THE 2-3 STANDARD DEVIATION BELOW  
AVERAGE AS THE OPPOSITE PHASE DOMINATES THE WRN U.S.  
 
00 UTC GEFS/ECMWF ENSEMBLES OFFER A WELL CLUSTERED FORECAST  
SOLUTION INTO DAY 6 OR SO THAT MAINTAINS MAX WPC CONTINUITY AND  
FORECAST CONFIDENCE. A FAVORED COMPOSITE SOLUTION LOCKS IN A FULL  
LATITUDE WRN NORTH AMERICAN RIDGE/ERN NORTH AMERICAN TROUGH  
PATTERN ALOFT. THE 00 UTC GEFS MAINTAINS THE WRN NOAM RIDGE MORE  
THAN THE 06 UTC GFS/00 UTC ECMWF ENSEMBLES DAY7/NEXT FRI AND THAT  
MAY BE A PRUDENT WAY TO GO GIVEN INITIAL AMPLITUDE. THIS WILL  
CONTINUE A SYNOPTIC PATTERN OVER THE U.S. WITH MILD/DRY CONDITIONS  
IN THE WEST...A TRANSITION ZONE OF TEMPS IN THE PLAINS TO MS  
VALLEY...AND COLD FLOW INTO THE ERN THIRD OF THE NATION WHERE  
HEAVY SNOW POTENTIAL WILL FOCUS FROM THE MIDWEST/GREAT LAKES TO  
THE NRN MID-ATLANTIC/NORTHEAST. DETERMINITSIC MODELS OFFER BETTER  
DETAIL BUT LESS RUN TO RUN CONTINUITY.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
THE PERSISTENT HIGH AMPLITUDE PATTERN OVER THE NATION...ABOVE  
NORMAL TEMPS REMAINS A FIXTURE OVER THE WRN U.S. WHILE COLD  
READINGS WILL DOMINATE EAST OF THE PLAINS. WHILE NO WIDESPREAD  
DAILY TEMPERATURES RECORDS SHOULD BE BROKEN...EXPECT ANOMALIES IN  
THE 10 TO 15 DEGREES ABOVE/BELOW NORMAL TO BE COMMONPLACE OVER  
THESE RESPECTIVE REGIONS. OVER SECTIONS OF THE NWRN U.S. INTO THE  
CENTRAL GREAT BASIN...UPPER/SURFACE RIDGING HELPS MAINTAIN A  
SEMI-PERMANENT LOW-LEVEL TEMP INVERSION. THUS...THESE LOCATIONS  
MAY STRUGGLE TO REACH SOME OF THE WARMER TEMPERATURES ACROSS  
SURROUNDING AREAS. OVER THE SWRN U.S...OFFSHORE SURFACE GRADIENTS  
IN RESPONSE TO INTERIOR HIGH PRESSURE MAY BRING FURTHER FIRE  
WEATHER CONCERNS TO SRN CA. A BIG STORY REMAINS A SNOWFALL THREATS  
FROM THE UPPER MIDWEST TO THE GREAT LAKES/OH VALLEY AND NERN U.S.  
COLD CYCLONIC FLOW OVER THE MILD GREAT LAKES WILL INVIGORATE HEAVY  
SNOW SHOWERS DOWNWIND. DEPENDING ON LOW DEPTH/PLACEMENT...A  
CONSIDERABLE SNOWFALL THREAT EXISTS FROM THE UPPER MIDWEST TO  
ESPECIALLY THE NERN STATES WITH TUE/WED.  
 
SCHICHTEL  
 

 
 
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