467  
FXUS02 KWBC 290656  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
155 AM EST MON NOV 29 2021  
 
VALID 12Z THU DEC 2 2021 - 12Z MON DEC 6 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 TO LOW AMPLITUDE TROUGHING 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 SOUTHEASTERN CANADA  
THROUGH FRIDAY WITH A TRAILING FRONT FOLLOWED BY A WEAKER LOW THIS  
WEEKEND, LEADING TO ROUNDS OF MAINLY LIGHT PRECIPITATION ACROSS  
THE GREAT LAKES AND NORTHEASTERN U.S. BY THE WEEKEND, SHOWERS AND  
SOME STORMS ARE LIKELY TO DEVELOP AHEAD OF A DEVELOPING STORM  
SYSTEM FROM THE GULF COAST TO THE OHIO VALLEY.  
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
THE 00Z GUIDANCE SUITE IS IN DECENT SYNOPTIC SCALE AGREEMENT  
THROUGH FRIDAY WITH AN UPPER RIDGE OVER THE SOUTHWESTERN U.S. AND  
A BROAD TROUGH OVER THE NORTHEAST U.S. AS THE FLOW PATTERN  
BECOMES MORE QUASI-ZONAL BY FRIDAY NIGHT AND INTO THE WEEKEND,  
MODEL SPREAD INCREASES WITH RESPECT TO THE NEXT SHORTWAVE TROUGH  
ENTERING THE NORTHWESTERN U.S., AS WELL AS A WEAK SOUTHERN STREAM  
UPPER LOW DEVELOPING OVER NORTHERN MEXICO, AND OVERALL FORECAST  
CONFIDENCE IS BELOW AVERAGE FOR THIS TIME PERIOD OWING TO  
SIGNIFICANT RUN-TO-RUN MODEL VARIATIONS. SOME OF THE GREATEST  
MODEL DIFFERENCES ARE WITH THE PAST FEW RUNS OF THE CMC THAT HAVE  
BEEN OUT OF PHASE ALONG THE WEST COAST FOR THE END OF THE FORECAST  
PERIOD AND QUALIFY AS OUTLIER SOLUTIONS COMPARED TO ENSEMBLE  
SPAGHETTI PLOTS FOR DAYS 6 AND 7. THEREFORE, THE WPC FORECAST WAS  
PRIMARILY BASED ON A GFS/ECMWF/UKMET BLEND THROUGH FRIDAY, AND  
THEN MAINLY ENSEMBLE MEANS WITH SOME OPERATIONAL GFS/ECMWF AND  
SOME PREVIOUS WPC CONTINUITY.  
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
WEATHER SHOULD BE RELATIVELY QUIET IN TERMS OF RAINFALL OR SNOW  
RELATED HAZARDS WITH NOT MUCH IN THE WAY OF HEAVY PRECIPITATION  
CURRENTLY EXPECTED THROUGH SATURDAY. ROUNDS OF RELATIVELY LIGHT  
PRECIPITATION ARE FORECAST FOR THE MIDWEST, GREAT LAKES, AND  
NORTHEAST WITH A PROGRESSIVE STORM TRACK OVER THE AREA. AMOUNTS  
SHOULD BE MOST SUBSTANTIAL IN FAVORED LAKE EFFECT AND POSSIBLY  
UPSLOPE AREAS, PARTICULARLY DOWNWIND OF LAKE ONTARIO INTO THE  
ADIRONDACKS. THEN MOISTURE IS SET TO INCREASE ACROSS THE SOUTHERN  
PLAINS AND LOWER MISSISSIPPI VALLEY LATE FRIDAY AND INTO THE  
WEEKEND, WHICH COULD LEAD TO SHOWERS AND THUNDERSTORMS BECOMING  
MORE WIDESPREAD THERE AND THEN EXTENDING NORTHEASTWARD AS THE  
SURFACE LOW OVER THE GREAT LAKES BECOMES BETTER ORGANIZED.  
 
TEMPERATURES ARE EXPECTED TO BE ABOVE NORMAL FOR THIS TIME OF YEAR  
ACROSS MOST OF THE NATION THROUGH NEXT WEEKEND, WITH THE GREATEST  
POSITIVE ANOMALIES EXPECTED FOR THE CENTRAL AND NORTHERN PLAINS  
WHERE BOTH HIGHS AND LOWS ARE FORECAST TO BE 15 TO 25+ DEGREES  
ABOVE AVERAGE FOR LATE IN THE WEEK. A FEW LOCATIONS MAY APPROACH  
DAILY MAXIMUM AND MINIMUM TEMPERATURE RECORDS WITH THESE MILD  
TEMPERATURES. BY THE WEEKEND, TEMPERATURES ARE CURRENTLY FORECAST  
TO MODERATE SOMEWHAT, BUT THIS IS SUBJECT TO CHANGE GIVEN FORECAST  
UNCERTAINTIES. NO ARCTIC AIRMASS INTRUSIONS ARE EXPECTED DURING  
THIS FORECAST PERIOD.  
 
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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