800  
FXUS02 KWBC 071610  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1110 AM EST THU DEC 07 2017  
 
VALID 12Z SUN DEC 10 2017 - 12Z THU DEC 14 2017  
   
..A MIDWEST/GREAT LAKES THROUGH NERN US HEAVY SNOW THREAT
 
 
...PATTERN OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT..  
 
THE 06 UTC GFS/GEFS AND 00 UTC ECMWF/ECMWF ENSEMBLES OFFER A WELL  
CLUSTERED FORECAST SOLUTION THAT IMPLIES BELOW NORMAL UNCERTAINTY  
OVERALL DESPITE MODEST RUN TO RUN VARIABLILITY. A FAVORED  
COMPOSITE SOLUTION LOCKS IN A FULL LATITUDE WRN NORTH AMERICAN  
RIDGE/ERN NORTH AMERICAN TROUGH PATTERN ALOFT. 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.  
 
THIS PATTERN WILL BE HIGHLIGHTED BY A SERIES OF POTENT SHORTWAVES  
AND ATTENDANT CLIPPER SYSTEMS/SNOW SWATHS THAT WILL DIG TO THE LEE  
OF THE WRN NOAM RIDGE TO THE UPPER MIDWEST AND MIDWEST/GREAT LAKES  
THEN OUT ACROSS THE ERN US WITHIN THE ERN US TROUGH. REINFORCED  
COLD AIR ADVECTION WILL ALSO ENHANCE LAKE EFFECT SNOWS IN THE WAKE  
OF SYSTEM PASSAGES THAT DO OFFER SOME TIMING VARIANCE. IN THE WAKE  
OF A NOW SHORT RANGE DEEPENED LOW TO EFFECT NEW ENGLAND AND  
CANADIAN MARITIMES THIS WEEKEND...ANOTHER UPSTREAM LOW ALSO HAS  
AMPLE POTENTIAL TO FURTHER DEVELOP AS A COASTAL STORM OFF THE NERN  
US TUE-WED AS ENERGY TRANSFERS OFFSHORE. MODELS AND ENSEMBLES ARE  
TRENDING TO SUPPORT A HEAVY SNOW THREAT IN THE COLD AIR  
ALONG/NORTH OF THE LOW TRACK FROM THE NRN MID-ATLANTIC TO THE  
NORTHEAST. MOISTURE IS RELATIVELY MODEST...BUT THE LOW AND SUPPORT  
ALOFT SEEM QUITE FAVORABLE.  
 
SCHICHTEL  
 

 
 
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