010  
FXUS02 KWBC 241904  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
203 PM EST WED NOV 24 2021  
 
VALID 12Z SAT NOV 27 2021 - 12Z WED DEC 01 2021  
   
..OVERVIEW
 
 
THE UPPER LEVEL PATTERN THIS WEEKEND INTO EARLY NEXT WEEK IS  
FORECAST TO BE AMPLIFIED AND FAIRLY STAGNANT WITH TROUGHING IN THE  
EAST AND RIDGING IN THE WEST, WITH THE EXCEPTION OF SOUTHERN  
STREAM ENERGY TRACKING ACROSS NORTHERN MEXICO AND TEXAS WHILE  
WEAKENING AND EVENTUALLY GETTING ABSORBED INTO THE EASTERN TROUGH.  
A COUPLE OF SHORTWAVES SHOULD INITIALLY HELP REINFORCE THE EASTERN  
TROUGH, WHILE BY TUESDAY-WEDNESDAY ADDITIONAL SHORTWAVES COMING  
INTO THE NORTH-CENTRAL U.S. MAY FLATTEN THE OVERALL UPPER PATTERN  
A BIT, BUT WITH SOME UNCERTAINTY.  
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
GUIDANCE CONTINUES TO SHOW REASONABLY GOOD AGREEMENT FOR THE 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 SLIGHT TIMING AND  
MAGNITUDE DIFFERENCES, WHICH AFFECTS A SURFACE LOW DEEPENING OFF  
THE NORTHEAST COAST. FOR THE 00/06Z MODEL CYCLE, THE ENSEMBLE  
MEANS CLUSTERED WELL WITH THE SURFACE LOW POSITION AROUND DAY  
5/MONDAY, AND WERE ALIGNED MOST CLOSELY TO THE 00Z ECMWF AND CMC  
AND 06Z GFS, SO THE WPC FORECAST MAINLY FAVORED THIS POSITION,  
WHICH WAS CLOSE TO CONTINUITY. THE 00Z GFS AND UKMET WERE FARTHER  
WEST/CLOSER TO THE COAST COMPARATIVELY, AND THE NEW 12Z GFS IS NOW  
SHOWING A DOUBLE BARRELED LOW SITUATION WITH A LOW CLOSER TO THE  
COAST AND ONE TO THE EAST, WHILE THE 12Z GEFS MEAN IS SLIGHTLY  
WESTWARD. MEANWHILE THE INCOMING 12Z ECWMF IS FARTHER SOUTH  
(AROUND THE LATITUDE OF THE NC/VA BORDER) WITH ITS LOW POSITION  
MONDAY MORNING BEFORE JUMPING NORTH TOWARD OTHER GUIDANCE, AGAIN  
SHOWING UNCERTAINTY. THE PLACEMENT OF THIS SURFACE LOW WILL HAVE  
IMPACTS FOR THE NORTHEAST INCLUDING HOW MUCH PRECIPITATION FALLS,  
SO THIS WILL CONTINUE TO BE MONITORED.  
 
DESPITE SOME DIFFERENCES, CONSENSUS NOW SHOWS TROUGHING IN THE  
EAST LIFTING SOMEWHAT ON TUESDAY INTO WEDNESDAY. THIS OCCURS AS  
SHORTWAVE ENERGY FROM CENTRAL CANADA THAT IN SOME PRIOR MODEL RUNS  
SERVED TO STRENGTHEN THE PREEXISTING TROUGH, AS WELL AS A  
SHORTWAVE COMING INTO THE PACIFIC NORTHWEST AROUND DAY 5/MONDAY  
AND PROPAGATING DOWNSTREAM, NOW FOR THE MOST PART APPEAR TO STAY  
SEPARATED FROM THE EASTERN TROUGHING. DIFFERENCES CERTAINLY REMAIN  
WITH THE TIMING AND POSITION OF THESE SHORTWAVES. WPC'S BLEND FOR  
THIS AREA AND FOR THE LATTER HALF OF THE MEDIUM RANGE PERIOD  
CONSISTED OF THE DETERMINISTIC 06Z GFS, ECWMF, AND CMC AS WELL AS  
THE GEFS AND EC MEAN, WHICH ADMITTEDLY WASHES OUT SOME SHORTWAVES  
BUT SEEMS TO BE THE BEST BET TO SMOOTH OUT DIFFERENCES CONSIDERING  
RUN-TO-RUN VARIABILITY.  
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
A PLUME OF MOISTURE/ATMOSPHERIC RIVER IS FORECAST TO TAKE AIM AT  
WESTERN CANADA AND INTO WASHINGTON ON SATURDAY, NORTH OF A LOW  
AMPLITUDE RIDGE. PRECIPITATION SHOULD REMAIN MOSTLY RAIN EVEN IN  
HIGHER ELEVATIONS FOR THIS EVENT DUE TO THE WARM TEMPERATURES,  
WITH HEAVIEST TOTALS LIKELY ALONG FAVORABLE TERRAIN. LIGHTER  
PRECIPITATION IS FORECAST TO CONTINUE IN THE PACIFIC NORTHWEST AND  
INTO THE NORTHERN ROCKIES THROUGH EARLY NEXT WEEK, BEFORE ANOTHER  
ROUND OF HEAVIER PRECIPITATION IS LIKELY FOR THE PACIFIC NORTHWEST  
AROUND TUESDAY-WEDNESDAY. MEANWHILE, LIGHT PRECIPITATION IS  
POSSIBLE WITH ENERGY MOVING THROUGH THE BASE OF THE TROUGH FOR THE  
MIDWEST/GREAT LAKES AND POSSIBLY THE OHIO VALLEY AND MID-ATLANTIC.  
PRECIPITATION (INCLUDING SOME SNOW) COULD BE ENHANCED DOWNWIND OF  
THE GREAT LAKES AND IN HIGHER ELEVATIONS, AND POSSIBLY IN EASTERN  
NEW ENGLAND ON THE BACKSIDE OF THE ATLANTIC SURFACE LOW. A COUPLE  
OF ROUNDS OF LIGHT RAIN ARE POSSIBLE IN TEXAS, WHILE MUCH OF THE  
REST OF THE COUNTRY LOOKS TO REMAIN DRY.  
 
THE MEAN TROUGH OVER THE EAST SHOULD KEEP TEMPERATURES BELOW  
NORMAL THROUGH MONDAY WITH SOME MODERATION BACK TOWARDS NORMAL ON  
TUESDAY AND WEDNESDAY. MEANWHILE, AMPLIFIED RIDGING WILL PROMOTE A  
WARMING TREND ACROSS THE WEST AND INTO THE PLAINS WITH SEVERAL  
DAYS OF +15 TO +25 ANOMALIES (LOCALLY HIGHER) LIKELY, ESPECIALLY  
ACROSS PARTS OF THE NORTHERN AND CENTRAL PLAINS SUNDAY AND MONDAY  
AND AGAIN ON WEDNESDAY.  
 
TATE/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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