223  
FXUS02 KWBC 051750  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1249 PM EST SUN NOV 05 2017  
 
VALID 12Z WED NOV 08 2017 - 12Z SUN NOV 12 2017  
 
...GUIDANCE/UNCERTAINTY ASSESSMENT AND WEATHER  
HIGHLIGHTS/THREATS...  
 
A WAVY TRAILING FRONT FROM THE WRN ATLC TO SRN/SERN US WILL FOCUS  
MODERATE TO HEAVY RAINS. POST-FRONTAL HIGH PRESSURE COOLS TEMPS IN  
ITS WAKE OVER THE W-CENTRAL TO ERN US. THERE REMAINS SOME  
POTENTIAL TO FURTHER DEVELOP EJECTING LOWS OFF THE EAST COAST UP  
TOWARD THE CANADIAN MARITIMES. SHORTWAVE SUPPORT FOR THIS HAS BEEN  
HIGHLY INCONSISTENT WITH RECENT GUIDANCE...BUT THE 06 UTC GFS AND  
00 UTC ECMWF NOW SHOW A SIMILAR SOLUTION ALOFT WITH ENERGY  
REACHING THE SERN US COAST THU...ENHANCING POTENTIAL. THAT  
SAID...THE 06 UTC GFS SEEMS TO OVER-DEVELOP SURFACE LOW RESPONSE  
LATER THU ONWARD DUE TO CONVECTIVE FEEDBACK.  
 
UPSTREAM...GUIDANCE DIGS AN AMPLIFIED CLOSED LOW/TROUGH OFF THE  
NWRN US INTO MIDWEEK WHOSE ENERGIES EJECT INLAND OVER THE WRN  
US/ROCKIES FRI/SAT ALONG WITH UNSETTLED WEATHER AND PCPN  
ENHANCEMENT. THIS INCLUDES PAC NW/NRN CA MODERATE TO HEAVY  
RAINS/MOUNTAIN SNOWS. TERRAIN ENHANCED HEAVY SNOWS SUBSEQUENTLY  
SPREAD INLAND ACROSS THE INTERMOUNTAIN WEST/ROCKIES THROUGH LATER  
WEEK. ENERGY/HEIGHT FALLS REACH THE PLAINS NEXT WEEKEND TO SPAWN  
FRONTOGENESIS/CYCLOGENESIS AS GRADUAL GULF OF MEXICO MOISTURE  
RETURN BECOMES AVAILABLE TO INCREASINGLY FUELS PRECIPITATION UP  
THROUGH THE CENTRAL THEN E-CENTRAL US AS A LEAD DOME OF COOLED  
WEDGED HIGH PRESSURE SLOWLY RECEDES EASTWARD. IN THIS  
PATTERN...ORGANIZED SNOWS ARE ALSO POSSIBLE OVER THE UPPER MIDWEST  
CONSIDERING FORECAST VERTICAL TEMP PROFILES NEXT WEEKEND AND  
GROWING LIFT/MOISTURE. WPC WINTER WEATHER OUTLOOK PROBABILITIES IN  
THE NDFD/WPC WEBSITE SHOW GROWING POTENTIAL.  
 
OVERTOP...A SERIES OF DYNAMIC SHIRTWAVES WILL MEANWHILE DIG  
UNDERNEATH A MEAN CLOSED HUDSON BAY LOW AND FORCE SEVERAL SURGES  
OF COLD CANADIAN AIR INTO THE N-CENTRAL AND NERN US TO FURTHER  
REINFORCE A COOLED MID-LATER NEXT WEEK AUTUMN PATTERN. THESE  
SURGES HAVE MODEST PCPN POTENTIAL/MOISTURE...BUT DO OFFER GREAT  
LAKE SNOW POTENTIAL AND COULD ACT TO INTERACT DOWNSTREAM WITH  
POTENTIAL LEAD WRN ATLANTIC LOWS.  
 
OVERALL...THE WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY DERIVED  
FROM A BLEND OF THE 06 UTC GFS/GEFS AND 00 UTC ECMWF/ECMWF  
ENSEMBLES THAT CLUSTER WELL ALOFT. HOWEVER...DUE TO THE  
AFOREMENTIONED APPARENT 06 UTC GFS CONVECTIVE FEEDBACK ISSUE BY  
LATER WEEK...PLACED MORE WEIGHTING ON THE ECMWF BY NEXT FRI-SUN.  
THE 12 UTC GFS HAS BACKED OFF FROM THIS SEEMINGLY ERRONEOUS 06 UTC  
GFS EAST COASTAL LOW.  
 
SCHICHTEL  
 

 
 
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