063  
FXUS02 KWBC 280653  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
152 AM EST SUN NOV 28 2021  
 
VALID 12Z WED DEC 1 2021 - 12Z SUN DEC 5 2021  
   
..OVERVIEW
 
 
THE OVERALL PATTERN WILL BE FEATURED BY AN UPPER LEVEL RIDGE FROM  
THE EASTERN PACIFIC TO THE INTERMOUNTAIN WEST, AND QUASI-ZONAL  
FLOW FROM THE PLAINS TO THE EAST COAST WITH MULTIPLE SHORTWAVE  
PERTURBATIONS PIVOTING AROUND A SYNOPTIC SCALE TROUGH OVER  
SOUTHEAST CANADA. THIS WILL INCLUDE AN ORGANIZED LOW PRESSURE  
SYSTEM TRACKING ACROSS SOUTHERN CANADA THROUGH FRIDAY WITH A  
TRAILING FRONT FOLLOWED BY A WEAKER LOW THIS WEEKEND. BY NEXT  
SUNDAY, ANOTHER STORM SYSTEM MAY DEVELOP ACROSS THE PLAINS ALONG A  
STRONG FRONTAL BOUNDARY.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
THE 00Z MODEL GUIDANCE SUITE BEGINS THE PERIOD ON WEDNESDAY WITH  
AVERAGE LEVELS OF AGREEMENT AND THEN BELOW AVERAGE FORECAST  
CONFIDENCE FOR LATE WEEK AND BEYOND. RECENT GFS RUNS HAVE BEEN  
QUITE VARIED REGARDING A SOUTHERN STREAM SHORTWAVE CROSSING THE  
GULF COAST REGION LATE IN THE WEEK, WITH LIMITED SUPPORT FROM THE  
ENSEMBLE MEANS. THERE HAS ALSO BEEN A FAIR AMOUNT OF MODEL  
RUN-TO-RUN VARIABILITY WITH THE ECMWF AS WELL ACROSS THE GREAT  
LAKES REGION AND THE DEGREE OF NORTHERN STREAM TROUGH AMPLITUDE.  
TOWARDS THE END OF THE FORECAST PERIOD, THE CMC IS MUCH STRONGER  
WITH AN EAST COAST TROUGH, ALTHOUGH NOT AS IMPRESSIVE AS ITS 12Z  
RUN. THERE IS ALSO A HIGH DEGREE OF MODEL SPREAD ALONG THE WEST  
COAST BY NEXT WEEKEND OWING TO A DISORGANIZED FLOW PATTERN OVER  
THE NORTHEAST PACIFIC AND POTENTIAL WEAKENING OF THE UPPER RIDGE  
AXIS.  
 
THE WPC FORECAST WAS PRIMARILY DERIVED FROM THE 12Z  
GFS/ECMWF/UKMET FOR WEDNESDAY AND THURSDAY, AND THEN MORE OF THE  
GEFS/EC MEANS THEREAFTER WHILE MAINTAINING 20-30 PERCENT OF THE  
PREVIOUS WPC FORECAST FOR PRESSURES IN ORDER TO MAINTAIN GOOD  
CONTINUITY.  
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
THINGS SHOULD BE RELATIVELY QUIET IN TERMS OF RAINFALL OR SNOW  
RELATED HAZARDS WITH NOT MUCH IN THE WAY OF HEAVY PRECIPITATION  
CURRENTLY EXPECTED. THE ACTIVE PATTERN FAVORING ATMOSPHERIC  
RIVERS OVER WASHINGTON STATE IN THE SHORT-RANGE PERIOD IS EXPECTED  
TO ABATE BY THURSDAY AS A SURFACE HIGH BUILDS OVER THE PACIFIC  
NORTHWEST AND BRITISH COLUMBIA. LIGHT TO MODERATE RAIN IS LIKELY  
FROM THE GREAT LAKES TO THE NORTHEAST THROUGH MID-WEEK OWING TO  
THE PROGRESSIVE STORM SYSTEM NEAR THE U.S./CANADA BORDER, FOLLOWED  
BY SOME LAKE EFFECT RAIN/SNOW SHOWERS TO CLOSE OUT THE WEEK.  
DEPENDING ON THE EVENTUAL STRENGTH AND LOCATION OF A POTENTIAL  
ORGANIZED LOW PRESSURE SYSTEM OVER THE PLAINS NEXT WEEK, SHOWERS  
AND SOME THUNDERSTORMS WILL BE POSSIBLE FROM THE GULF COAST TO THE  
MIDWEST.  
 
TEMPERATURES ARE EXPECTED TO BE WELL ABOVE NORMAL FOR THIS TIME OF  
YEAR ACROSS THE WESTERN U.S. AND THE PLAINS THROUGH THE END OF THE  
WEEK OWING TO THE RIDGE ALOFT, AND CLOSER TO NORMAL FOR THE EAST  
COAST ON WEDNESDAY FOLLOWED BY A WARMING TREND FOR THURSDAY AND  
FRIDAY. BOTH HIGHS AND LOWS ARE FORECAST TO BE 15 TO 25+ DEGREES  
ABOVE AVERAGE FOR NORTHERN AND CENTRAL PORTIONS OF THE HIGH PLAINS  
AND EXPANDING INTO THE MIDWEST FOR WEDNESDAY AND THURSDAY. A FEW  
LOCATIONS MAY APPROACH DAILY MAXIMUM AND MINIMUM TEMPERATURE  
RECORDS WITH THESE MILD TEMPERATURES. HOWEVER, IT IS WORTH NOTING  
THAT SUBSTANTIAL CHANGES TO THE FORECAST ARE POSSIBLE GOING  
FORWARD GIVEN THE UNCERTAINTIES NOTED IN RECENT MODEL RUNS.  
 
HAMRICK  
 
ADDITIONAL 3-7 DAY HAZARD INFORMATION CAN BE FOUND ON THE WPC  
MEDIUM RANGE HAZARDS OUTLOOK CHART AT:  
 
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP  
 
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, WINTER WEATHER OUTLOOK PROBABILITIES  
AND HEAT INDICES ARE AT:  
 
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML  
 

 
 

 
 
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