597  
FXUS02 KWBC 281900  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
200 PM EST SUN NOV 28 2021  
 
VALID 12Z WED DEC 01 2021 - 12Z SUN DEC 05 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 SOUTHERN CANADA THROUGH FRIDAY  
WITH A TRAILING FRONT FOLLOWED BY A WEAKER LOW THIS WEEKEND,  
LEADING TO ROUNDS OF LIGHT TO MODERATE PRECIPITATION ACROSS THE  
NORTH-CENTRAL AND NORTHEASTERN U.S. BY THE WEEKEND, MOIST INFLOW  
IS EXPECTED TO RETURN TO THE SOUTH-CENTRAL U.S., BRINGING  
INCREASED RAIN CHANCES AS THE MOISTURE FOCUSES ALONG A FRONTAL  
BOUNDARY.  
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
THE 00/06Z MODEL CYCLE BEGINS THE MEDIUM RANGE PERIOD WEDNESDAY  
WITH FAIRLY GOOD AGREEMENT WITH THE LARGE SCALE PATTERN: RIDGING  
THROUGH WESTERN PARTS OF THE U.S. WHILE SHORTWAVES (WITH VARYING  
INTENSITIES DEPENDING ON THE MODEL) PASS THROUGH MILD TROUGHING IN  
CENTRAL/EASTERN PARTS OF THE COUNTRY. A PARTICULARLY STRONG  
SHORTWAVE WILL PUSH A SURFACE LOW THROUGH SOUTHERN CANADA  
WEDNESDAY-THURSDAY WITH REASONABLY GOOD AGREEMENT IN POSITION. GFS  
RUNS WERE THE STRONGEST WITH A SHORTWAVE TRACKING QUICKLY THROUGH  
THE SOUTHEAST LATE WEDNESDAY INTO THURSDAY, WHICH WAS NOT  
PARTICULARLY FAVORED. MAGNITUDE AND POSITIONING OF SHORTWAVES  
CONTINUE TO BE THE BIGGEST FORECAST CHALLENGE FRIDAY INTO THE  
WEEKEND AS WELL, CAUSING SOME UNCERTAINTIES TO ARISE EVEN WITHIN  
THE BROADER FLOW BY THE WEEKEND. IN GENERAL THE FLOW BY THE  
WEEKEND HAS TRENDED LESS AMPLIFIED COMPARED TO MODEL GUIDANCE,  
WITH THE EXCEPTION OF A SOUTHERN STREAM UPPER LOW TRENDING A  
LITTLE STRONGER ACROSS NORTHERN MEXICO BY SUNDAY, AND AT THIS  
POINT IT DOES NOT APPEAR THERE ARE CLEAR OUTLIERS WITH THE OVERALL  
PATTERN. THUS THE WPC FORECAST WAS BASED INITIALLY ON A BLEND OF  
DETERMINISTIC GUIDANCE OF THE 00Z/06Z GFS AND 00Z ECMWF, UKMET,  
AND CMC, PHASING TOWARD A BLEND OF THE MODELS AND GEFS AND EC  
ENSEMBLE MEANS BY THE END OF THE PERIOD, ALONG WITH SOME  
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. GENERALLY MODERATE PRECIPITATION LINGERING IN  
THE PACIFIC NORTHWEST, PARTICULARLY THE OLYMPIC PENINSULA AND  
NORTHERN CASCADES, SHOULD ABATE FOR THE LATTER PART OF THE WEEK AS  
A SURFACE HIGH BUILDS OVER THE PACIFIC NORTHWEST AND BRITISH  
COLUMBIA, BEFORE PRECIPITATION CHANCES INCREASE AGAIN FOR THE  
WEEKEND. 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 RAIN  
BECOMING MORE WIDESPREAD THERE AND NORTHEASTWARD DEPENDING ON  
POSSIBLE LOW PRESSURE AND FRONTAL SYSTEM DEVELOPMENT.  
 
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. BY THE WEEKEND, TEMPERATURES  
ARE CURRENTLY FORECAST TO MODERATE SOMEWHAT, BUT THIS IS SUBJECT  
TO CHANGE GIVEN FORECAST UNCERTAINTIES.  
 
TATE/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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