068  
FXUS02 KWBC 180652  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
152 AM EST SAT NOV 18 2017  
 
VALID 12Z TUE NOV 21 2017 - 12Z SAT NOV 25 2017  
   
..GUIDANCE/UNCERTAINTY PREFERENCES...
 
 
A DYNAMIC LEAD MID-UPPER LEVEL TROUGH/HEIGHT FALLS PROGRESS FROM  
THE UPPER MIDWEST THROUGH THE GREAT LAKES/NERN US TUE-WED WITHIN  
NRN STREAM FLOW. THIS SUPPORTS A DEEPENED CLIPPER LOW TRACK AND  
SWATH OF PCPN ALONG THE US/CANADIAN BORDER ALONG WITH A  
REINFORCING COOLING SURGE AND A PERIOD OF LAKE EFFECT SNOWS IN THE  
WAKE OF SYSTEM PASSAGE. SEVERAL LESS CERTAIN WEAKER PROGRESSIVE  
SYSTEMS ARE SLATED TO FOLLOW LATER NEXT WEEK WITHIN THIS NRN  
STREAM FLOW.  
 
THE EXTENT OF DIGGING OF EMBEDDED SRN STREAM IMPULSES UNDERNEATH  
TO THE LEE OF A BUILDING WARMING WRN US MID-UPPER LEVEL RIDGE  
EARLY NEXT WEEK AND MID-LATER NEXT WEEK POTENTIAL SRN STREAM  
TROUGH/LOW SEPARATION OVER THE GULF COAST REMAINS FURTHER  
COMPLICATED BY POTENTIAL FOR NRN STREAM INTERACTION IN SOME  
SOLUTIONS. FORECAST SPREAD AND UNCERTAINTY REMAINS ABOVE NORMAL  
ALONG WITH MODEL RUN TO RUN VARIANCE. OF THE ENSEMBLES...PREFER  
THE ECENS THAT SHOWS MORE FLOW SEPARATION AND WEATHER FOCUS THAN  
THE GEFS/CANADIAN/NAEFS. THIS MATCHES WPC CONTINUITY AND FITS THE  
OVERALL FLOW AMPLIFICATION UPSTREAM AS PER RECENT MODEL TRENDS.  
 
MEANWHILE...CONTINUED INLAND FLOW OF PACIFIC IMPULSES FROM AN  
AMPLIFIED OFFSHORE MID-UPPER LEVEL MEAN TROUGH PROLONGS A WET  
PATTERN THAT INCLUDES ELEVATION SNOWS OVER THE NWRN US THROUGH THE  
EXTENDED THANKSGIVING BREAK...ALBEIT WITH QUICKLY GROWING TIMING  
UNCERTAINTY.  
 
OVERALL...THE WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY DERIVED  
FROM A BLEND OF THE 12 UTC GFS/ECMWF AND GEFS/ECMWF ENSEMBLES INTO  
THANKSGIVING BEFORE TRANSITIONING TO AN ECMWF ENSEMBLE MEAN  
CENTERED SOLUTION BY DAYS 6/7 (NEXT FRI-SAT) THAT MAINTAINS MAX  
WPC CONTINUIY.  
 
   
..WEATHER HIGHLIGHTS
 
 
WET FLOW CONTINUES FOR THE PACIFIC NW WITH OCCASIONALLY HEAVY  
DAILY RAINS AND LOCALLY HEAVY ELEVATION SNOWS. UPPER RIDGING WILL  
SUPPORT ABOVE AVERAGE TEMPERATURES FROM THE SOUTHWEST THROUGH THE  
SOUTHERN GREAT BASIN/ROCKIES AND PLAINS...BUT COOLER THAN AVERAGE  
IN THE EASTERN US BEHIND A COLD FRONT. THERE IS A GOOD CHANCE FOR  
APPRECIABLE PRECIPITATION ALONG THE GULF COAST AS LOW PRESSURE  
MEANDERS ALONG A SLOW MOVING FRONT. EXPECT SOME RAIN/SNOW AROUND  
THE GREAT LAKES BUT GENERALLY NO PRECIPITATION FROM THE SOUTHWEST  
TO THE PLAINS AND MS VALLEY.  
 
   
..THANKSGIVING FORECAST
 
 
GENERALLY QUIET FOR MOST OF THE LOWER 48. PRECIPITATION WILL BE  
MOST CONCENTRATED IN THE PACIFIC NORTHWEST INTO NORTHERN  
CALIFORNIA AS WELL AS NORTHERN IDAHO/WESTERN MONTANA/NW WYOMING.  
ORGANIZED RAIN IS ALSO QUITE POSSIBLE ALONG THE GULF COAST FROM  
TEXAS EASTWARD TO FLORIDA . RECORD HIGH TEMPS ARE POSSIBLE IN THE  
SOUTHWEST WITH WIDESPREAD 80S AND SOME 90S.  
 
SCHICHTEL  
 

 
 
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