816  
FXUS02 KWBC 250650  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
150 AM EST THU NOV 25 2021  
 
VALID 12Z SUN NOV 28 2021 - 12Z THU DEC 02 2021  
   
..OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
MEAN TROUGHING IN THE EAST WILL BE REINFORCED SEVERAL TIMES BY  
SHORTWAVES AND MAINTAINED THROUGHOUT MUCH OF THE MEDIUM RANGE  
PERIOD (SUNDAY-THURSDAY). ELSEWHERE, AN AMPLIFIED RIDGE ACROSS THE  
WEST SHOULD WEAKEN AS A COUPLE OF SHORTWAVES MOVE THROUGH AND INTO  
THE CENTRAL U.S., WHICH SHOULD ALSO HELP TO FLATTEN THE OVERALL  
UPPER PATTERN SOME BY MID TO LATER NEXT WEEK.  
 
THE GUIDANCE CONTINUES TO SHOW REASONABLY GOOD AGREEMENT FOR THIS  
LARGE SCALE FLOW PATTERN BUT OFFERS PLENTY OF UNCERTAINTY STILL IN  
THE DETAILS. ENERGY RELOADING THROUGH THE WESTERN SIDE OF THE  
TROUGH IN THE EAST ON SUNDAY-MONDAY CONTINUES TO SHOW SOME TIMING  
AND MAGNITUDE DIFFERENCES, WHICH WOULD AFFECT A SURFACE LOW  
DEEPENING OFF THE NORTHEAST COAST. THE 18Z YESTERDAY (AND TODAYS  
00Z) GFS CONTINUES TO BE STRONGEST/DEEPEST WITH THE UPPER LOW  
WHILE THE 12Z/YESTERDAY ECMWF INTIALLY KEEPS A SURFACE LOW FARTHER  
SOUTH ALONG THE MID-ATLANTIC COAST BEFORE JUMPING NORTH AND MORE  
IN LINE WITH THE OTHER SOLUTIONS. THE ENSEMBLE MEANS SEEM TO OFFER  
A SOLUTION CLUSTERED CLOSER TO THE GFS/CMC/UKMET WHICH IS WHAT WPC  
FAVORED TONIGHT. REGARDLESS, THE PLACEMENT OF THIS SURFACE LOW  
WILL HAVE IMPACTS FOR THE NORTHEAST INCLUDING HOW MUCH  
PRECIPITATION FALLS, SO THIS WILL NEED TO BE MONITORED.  
 
OUT WEST, A WEAK SHORTWAVE INTO THE WEST COAST AROUND MONDAY NEXT  
WEEK SHOULD PROPAGATE EASTWARD INTO THE CENTRAL PLAINS AND  
EVENTUALLY THE EAST BY THE MIDDLE TO LATTER PART OF NEXT WEEK. THE  
LAST COUPLE OF MODEL RUNS INDICATE THERE'S PLENTY OF UNCERTAINTY  
REMAINING WITH THIS SYSTEM, ESPECIALLY THE LATTER HALF OF THE  
PERIOD MAINLY TIMING AND INTENSITY AND HOW IT INTERACTS WITH THE  
EASTERN TROUGH ALREADY IN PLACE. A BLEND TOWARDS THE ENSEMBLE  
MEANS LATER IN THE PERIOD SEEMED TO MITIGATE THESE DIFFERENCES  
WELL UNTIL THESE DETAILS CAN BE IRONED OUT IN FUTURE RUNS.  
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
THE ATMOSPHERIC RIVER INTO THE PACIFIC NORTHWEST SHOULD BE  
WEAKENING BY SUNDAY, THOUGH SOME LINGERING MODERATE TO LOCALLY  
HEAVY RAINFALL WILL REMAIN POSSIBLE ACROSS THE OLYMPIC PENINSULA  
AND FAR NORTHERN CASCADES. WESTERLY FLOW ACROSS THE GREAT LAKES  
SHOULD CONTINUE TO SUPPORT LAKE EFFECT SNOWFALL WITH SOME LIGHT TO  
MODERATE ACCUMULATIONS POSSIBLE SUNDAY INTO MONDAY. MODELS SHOW  
THE HEAVIEST RAINFALL ASSOCIATED WITH THE EARLY PERIOD NORTHEAST  
SURFACE LOW SHOULD MAINLY REMAIN OFFSHORE, BUT WRAP AROUND LIGHT  
SNOW OR COASTAL RAIN MAY BE POSSIBLE. AN UPPER LOW CAMPED OUT WEST  
OF BAJA CALIFORNIA MAY HELP FUNNEL MOISTURE TOWARDS THE GULF COAST  
REGION, BUT ASSOCIATED PRECIPITATION SHOULD BE LIGHT AND SCATTERED  
IN NATURE. AFTER MONDAY, CONDITIONS ACROSS THE CONUS SHOULD BEGIN  
TO DRY OUT FOR MOST REGIONS AS THE FLOW BECOMES LESS AMPLIFIED.  
THE EXCEPTION TO THIS MAY BE ACROSS THE PACIFIC NORTHWEST WHERE  
TROUGHING IN THE NORTHEAST PACIFIC SHOULD KEEP A CONSISTENT FOCUS  
OF MOISTURE INTO THE REGION.  
 
THE MEAN TROUGH OVER THE EAST SHOULD KEEP TEMPERATURES SLIGHTLY  
BELOW NORMAL INTO TUESDAY WITH SOME MODERATION BACK TOWARDS NORMAL  
WEDNESDAY AND THURSDAY. MEANWHILE, UPPER LEVEL RIDGING KEEPS  
CONDITIONS WARM THROUGHOUT THE WEST AND CENTRAL U.S. THE ENTIRE  
PERIOD, WITH A HANDFUL OF BOTH RECORD HIGHS AND WARM OVERNIGHT  
LOWS POSSIBLE. THE GREATEST ANOMALIES SHOULD BE ACROSS THE  
NORTHERN-CENTRAL PLAINS WHERE DAYTIME HIGHS COULD BE 20 TO 30  
DEGREES ABOVE NORMAL. AS THE FLOW FLATTENS DURING THE LATE PERIOD,  
ABOVE NORMAL TEMPERATURES SHOULD ALSO BEGIN EXPANDING INTO THE  
MIDWEST AND SOUTH.  
 
SANTORELLI  
 
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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