128  
FXUS02 KWBC 230658  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
157 AM EST TUE NOV 23 2021  
 
VALID 12Z FRI NOV 26 2021 - 12Z TUE NOV 30 2021  
 
   
..OVERVIEW
 
 
THE MEDIUM RANGE SHOULD REMAIN VERY AMPLIFIED IN THE UPPER LEVELS  
THROUGH THE ENTIRE PERIOD. A CLOSED SOUTHERN STREAM LOW OVER BAJA  
CALIFORNIA LOOKS TO LINGER FOR A FEW DAYS BEFORE WEAKENING AND  
ATTEMPTING TO LIFT INTO THE SOUTHWEST EARLY NEXT WEEK. MEANWHILE,  
A CLOSED LOW OVER THE GREAT LAKES WILL LIFT INTO THE NORTHEAST  
WHILE ADDITIONAL ENERGY FROM THE WEST SHOULD ACT TO RELOAD AND  
AMPLIFY THE TROUGH OVER THE EASTERN U.S. BY EARLY NEXT WEEK. UPPER  
LEVEL RIDGING WILL BUILD ACROSS THE NORTHWEST/ROCKIES THIS WEEKEND  
AND EARLY NEXT WEEK AS THE NEXT SYSTEM APPROACHES THE WEST COAST  
BY TUESDAY.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
LATEST GUIDANCE CONTINUES TO SHOW ABOVE AVERAGE AGREEMENT ON THE  
LARGE SCALE FLOW THROUGH MOST OF THE PERIOD. THE GREATEST  
UNCERTAINTIES IN THE FORECAST LIE WITH REINFORCING ENERGY INTO THE  
EAST THIS WEEKEND AND EARLY NEXT WEEK, WHERE THE GUIDANCE  
CONTINUES TO SHOW VARYING SOLUTIONS ON THE DETAILS AND EVOLUTION  
OF THE TROUGH. THE MODELS INDICATE THE POTENTIAL FOR ANOTHER  
SURFACE LOW TO SPIN UP AND DEEPEN OFF THE NORTHEAST COAST BUT  
AGAIN, TIMING AND STRENGTH OF THIS LOW ARE AN ISSUE. THE CMC IS  
THE FARTHEST NORTH LIFTING THE LOW TOWARDS THE NORTHWEST ACROSS  
MAINE ON TUESDAY, WHICH THE ECMWF AND GFS ARE NOTABLY FARTHER  
SOUTH AND MORE OFFSHORE (GFS FARTHEST OFFSHORE). THE RUN TO RUN  
VARIABILITY IN THE DETERMINISTIC SOLUTIONS REMAINS ALL OVER THE  
PLACE THOUGH SO CONFIDENCE IN THE SPECIFICS IS LOW WITH THIS  
SYSTEM. THE ENSEMBLE MEANS ARE WEAKER, AS EXPECTED, WITH THE LOW  
BUT DO PROVIDE A NICE MIDDLE GROUND SOLUTION AT THIS TIME.  
ELSEHWERE, THERE ARE ALSO TIMING AND AMPLITUDE DIFFERENCES WITH  
THE APPROACHING TROUGH INTO THE WEST ON DAY 7.  
 
WPC USED A GENERAL MODEL BLEND FOR DAYS 3-5, WITH INCREASING  
CONTRIBUTIONS FROM THE ENSEMBLE MEANS BY LATE PERIOD. THIS SHOULD  
HELP TO MITIGATE DIFFERENCES DISCUSSED ABOVE. THIS COMBINATION  
MAINTAINS GOOD CONTINUITY WITH THE PREVIOUS WPC FORECAST FOR DAYS  
3-6.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
A COLD FRONT EXITING THE EAST COAST AS THE PERIOD BEGINS FRIDAY  
MAY CONTINUE TO BRING SOME LIGHT TO MODERATE PRECIPITATION TO  
PARTS OF THE NORTHEAST AS WELL AS THE GREAT LAKES. FAVORABLE  
WESTERLY FLOW OVER THE STILL RELATIVELY WARMER LAKES SHOULD RESULT  
IN AT LEAST MODEST LAKE EFFECT SNOW ACCUMULATIONS MAINLY DOWNWIND  
OF LAKES ERIE AND ONTARIO ON FRIDAY INTO SATURDAY. ANOTHER WEAK  
SHORTWAVE SHOULD HELP DIRECT A PLUME OF MOISTURE INTO THE PACIFIC  
NORTHWEST THIS WEEKEND, POSSIBLY BRINGING ANOTHER ROUND OF  
MODERATE TO LOCALLY HEAVY RAINS TO PARTS OF WESTERN WASHINGTON,  
WITH THE HEAVIEST TOTALS LIKELY ALONG FAVORABLE TERRAIN. LIGHTER  
PRECIPITATION SHOULD SPILL OVER INTO PARTS OF THE NORTHWEST AND  
ROCKIES AS WELL THIS WEEKEND BUT QUICKLY DRY OUT EARLY NEXT WEEK.  
THE REMAINDER OF THE COUNTRY SHOULD REMAIN FAIRLY DRY THROUGH THE  
WEEKEND AND INTO NEXT WEEK. A WEAK SYSTEM MOVING THROUGH THE OHIO  
VALLEY INTO THE EAST MAY BRING SOME LIGHT PRECIPITATION TO THE  
REGION BUT NOTHING LOOKS PARTICULARLY IMPACTFUL AT THIS TIME.  
 
A BUILDING TROUGH OVER THE EAST SHOULD KEEP TEMPERATURES BELOW  
NORMAL THROUGH THE ENTIRE FIVE DAY PERIOD WITH THE GREATEST  
ANOMALIES (-10 TO -15F) LIKELY ON FRIDAY INTO SATURDAY FROM SOUTH  
TEXAS/LOWER MISSISSIPPI VALLEY TO THE OHIO VALLEY AND  
MID-ATLANTIC. MEANWHILE, AMPLIFIED RIDGING WILL PROMOTE A WARMING  
TREND ACROSS THE WEST AND INTO THE PLAINS WITH SEVERAL DAYS OF +10  
TO +20 ANOMALIES (LOCALLY HIGHER) LIKELY, ESPECIALLY ACROSS PARTS  
OF THE NORTHERN AND CENTRAL HIGH PLAINS SUNDAY AND MONDAY.  
 
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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