883  
FXUS02 KWBC 231601  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1200 PM EDT MON OCT 23 2017  
 
VALID 12Z THU OCT 26 2017 - 12Z MON OCT 30 2017  
 
...GUIDANCE/UNCERTAINTY ASSESSMENT AND WEATHER/THREATS  
HIGHLIGHTS...  
 
MODELS AND ENSEMBLES SEEM IN REASONABLE OVERALL AGREEMENT THU/FRI  
AS A WELL ORGANIZED LEAD SYSTEM EJECTS OFF THE ERN SEABOARD INTO  
THE CANADIAN MARITIMES AND WRN ATLANTIC. THIS OCCURS AS A DYNAMIC  
UPSTREAM MID-UPPER LEVEL TROUGH DIGS SEWD OVER THE N-CENTRAL US IN  
RAPIDLY AMPLIFYING MID-UPPER LEVEL FLOW DOWNSTREAM OF A BUILDING  
NORTH AMERICAN WEST COAST RIDGE. AN ASSOCIATED AND PCPN FOCUSING  
SURFACE LOW DEVELOPS AND LIFTS ACROSS THE UPPER MIDWEST/GREAT  
LAKES INTO ERN CANADA DURING THIS PERIOD...WITH ADDITIONAL  
ACTIVITY ALONG/AHEAD OF A TRAILING COLD FRONT AS POST-FRONTAL COLD  
HIGH PRESSURE SURGES RAPIDLY DOWN THROUGH THE W-CENTRAL US.  
 
GUIDANCE FORECAST SPREAD INCREASES MORE SIGNIFICANTLY OVER THE  
WEEKEND INTO EARLY NEXT WEEK...EVEN THOUGH THERE IS DECENT  
AGREEMENT WITH THE IDEA OF SWINGING AN ELONGATED AND WIDESPREAD  
RAINFALL FOCUSING FRONT ACROSS THE ERN US. POTENTIAL WAVE  
DEVELOPMENT DETAILS ARE MORE UNCERTAIN...BUT OVERALL DOES SEEM  
LIKELY GIVEN SUPPORTING MID-UPPER LEVEL TROUGH AMPLITUDE ALOFT.  
MODELS AND ENSEMBLES ALSO INTRODUCE A THREAT OF A POTENTIAL  
CARRIBEAN TROPICAL SYSTEM DEVELOPING AND LIFTING UP OFF THE ERN  
SEABOARD IN ADVANCE OF THE WAVY AND SLOWLY EASTWARD PROGRESSING  
FRONTAL SYSTEM. THIS WOULD HAVE SOME POTENTIAL TO DRASTICALLY  
INCREASE AVAILABLE MOISTURE/PCPN INTO THE WRN ATLANTIC AND  
POSSIBLY THE ERN US. SATELLITE IMAGERY DOES NOT HAVE A CLEAR  
SIGNAL FOR DEVELOPMENT YET...BUT SOME MODELS INCLUDING ESPECIALLY  
THE 00 UTC ECMWF/CANADIAN AND UKMET OFFER MORE ORGANIZED AND  
INCREASINGLY FAST PROPAGATION THAN THE GFS...A WIDE VARIETY OF  
ENSEMBLE MEMBERS...AND NHC/WPC CONTINUITY. WPC PROGS FOCUS  
ACTIVITY WITH THE WAVY FRONT AND ARE MORE CONSERVATIVE WITH  
TROPICAL DEVELOPMENTS PENDING INCREASED SATELLITE/GUIDANCE SIGNALS  
AND ADDITIONAL NHC COLLABORATION.  
 
OVERALL...WPC MEDIUM RANGE SURFACE FRONTS PRESSURES AND 500MB  
PROGS WERE ACCORDINGLY DERIVED MAINLY FROM THE 00 UTC ECMWF  
ENSEMBLE MEAN ALONG WITH SMALLER INPUTS FROM THE 06 UTC GFS/GEFS  
AND 00 UTC ECMWF TO INCORPORATE SOME OF THE ENVELOPE OF GUIDANCE  
SOLUTIONS.  
 
SCHICHTEL  
 

 
 
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