604  
FXUS02 KWBC 020547  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
146 AM EDT THU NOV 02 2017  
 
VALID 12Z SUN NOV 05 2017 - 12Z THU NOV 09 2017  
   
..OVERVIEW
 
 
UPPER PATTERN OVER THE CONUS WILL BE DRIVEN BY AN UPPER RIDGE OVER  
MEXICO AND WELL UPSTREAM OVER ALASKA WITH TROUGHING IN BETWEEN --  
ROUGHLY OVER THE NORTHWEST. A COUPLE OF SYSTEMS WILL PUSH THROUGH  
THE WEST DURING THE PERIOD WITH COOLER TEMPERATURES AND FAIRLY  
WIDESPREAD RAIN AND MOUNTAIN SNOW. THE EASTERN STATES WILL TREND  
TOWARD LOWER HEIGHTS AS A LEAD FRONT PUSHES OFF THE COAST ON  
MONDAY WITH A POSSIBLE WAVE ALONG THE FRONT LIFTING OUT THROUGH  
THE MID-ATLANTIC NEXT WEEK.  
 
   
..GUIDANCE/UNCERTAINTY ASSESSMENT
 
 
THE MODELS AND ENSEMBLES REMAIN WELL-CLUSTERED TO START THE  
FORECAST ON SUNDAY BUT WITH LINGERING DIFFERENCES IN HOW THE  
SYSTEM OVER THE CENTRAL PLAINS LIFTS INTO CANADA. BY ABOUT TUESDAY  
THE ENSEMBLES SHOW SOME NOTABLE DIFFERENCES IN WHERE THE SFC FRONT  
LIES OVER THE MID-MS AND TENNESSEE VALLEY AS WELL AS HOW THE  
WESTERN SHORTWAVE OR UPPER LOW EJECTS THROUGH THE CENTRAL/NORTHERN  
ROCKIES. THE 12Z ECMWF/CANADIAN WERE SLOWER THAN THE 12Z GFS/UKMET  
AND OLDER 00Z/01 ECMWF WHILE THE ENSEMBLES GENERALLY LIED IN THE  
MIDDLE (18Z GEFS AND 12Z ECMWF ENSEMBLE MEAN). THOUGH SEVERAL  
ECMWF ENSEMBLES WERE NEAR THE SLOWER ECMWF/CANADIAN, PAST FEW RUNS  
WERE NOT AS SLOW AND MULTI-DAY TRENDS WITH THE WESTERN TROUGH IN  
GENERAL HAS BEEN QUICKER, SO OPTED TO STICK WITH THE LARGER  
CONSENSUS AROUND THE OLDER 00Z/01 ECMWF, 12Z/01 GFS, AND  
ESPECIALLY THE 12Z/01 ECMWF ENSEMBLE MEAN (WHICH HAS BEEN A BIT  
BETTER THAN THE GEFS MEAN IN THIS RECENT PATTERN). FARTHER EAST,  
MODELS HAVE REALLY STRUGGLED WITH HOW TO EVOLVE THE STATIONARY  
BOUNDARY AND POSSIBLE SFC WAVE MIDWEEK (RELATED TO UPSTREAM  
DIFFERENCES OUT OF THE WEST). LARGE E-W DIFFERENCE BOUNDED BY THE  
SLOWER ECMWF AND QUICKER CANADIAN YIELDED AND ENSEMBLE-BASED  
SOLUTION NOT TOO UNLIKE THE 18Z GFS. CONFIDENCE IS LOW IN THE  
DETAILS DESPITE BEING NO WORSE THAN AVERAGE ON THE LARGER SCALE  
PATTERN.  
 
   
..WEATHER/THREAT HIGHLIGHTS
 
 
ARCTIC HIGH SLIPPING SOUTHEASTWARD ACROSS MONTANA INTO THE HIGH  
PLAINS WILL KEEP BELOW AVERAGE TEMPERATURES OVER MOST OF BIG SKY  
COUNTRY. QUITE THE OPPOSITE WILL BE TRUE SOUTH OF THE FRONT ACROSS  
THE SOUTHERN PLAINS INTO THE SOUTHEAST WHERE TEMPERATURES ARE  
EXPECTED TO BE 10-20 DEGREES ABOVE AVERAGE. PRECIPITATION WILL  
FOCUS ALONG THE PROGRESSIVE FRONT FROM THE MIDWEST TO THE  
NORTHEAST SUN/MON AND ALSO ACROSS THE INTERIOR WEST TO THE ROCKIES  
WITH UPSLOPE FLOW. A BREAK ON TUE OR WED FOR THE WEST MAY BE  
FOLLOWED BY ANOTHER SYSTEM NEXT THURSDAY WITH PRECIPITATION  
SPREADING THROUGH WA/OR/ID. IN THE EAST, PRECIPITATION WILL BE  
ENHANCED AROUND THE SFC WAVE AS IT MOVES INTO THE ATLANTIC.  
POSSIBILITY EXISTS FOR A SWATH OF MODERATE TO HEAVY RAIN SHOULD IT  
DEVELOP AS MUCH AS SOME MODELS DEPICT.  
 
FRACASSO  
 

 
 
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