152  
FXUS02 KWBC 240656  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
155 AM EST WED NOV 24 2021  
 
VALID 12Z SAT NOV 27 2021 - 12Z WED DEC 01 2021  
   
..OVERVIEW
 
 
THE UPPER LEVEL FLOW DURING THE MEDIUM RANGE PERIOD SHOULD REMAIN  
MOSTLY STAGNANT AND AMPLIFIED CONSISTING OF MEAN TROUGHING IN THE  
EAST AND RIDGING OUT WEST. A SOUTHERN STREAM UPPER LOW OVER BAJA  
CALIFORNIA ON SATURDAY SHOULD WEAKEN WITH THE LEFTOVER ENERGY  
SHIFTING INTO THE SOUTHERN PLAINS AND EVENTUALLY BEING ABSORBED BY  
THE EASTERN U.S. TROUGH. A COUPLE OF SHORTWAVES INTO THE EASTERN  
TROUGH SHOULD HELP REINFORCE IT THROUGH THE PERIOD. GENERAL  
RIDGING SHOULD PERSIST OUT WEST, THOUGH PERIODICALLY MAY BE  
INTERRUPTED BY WEAK WAVES OF SHORTWAVE ENERGY.  
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
GUIDANCE CONTINUES TO SHOW GOOD AGREEMENT ON THE LARGE SCALE FLOW  
PATTERN BUT OFFER PLENTY OF UNCERTAINTY STILL IN THE DETAILS.  
EARLY ON, THERE ARE SOME TIMING/INTENSITY DIFFERENCES WITH  
RELOADING ENERGY INTO THE EASTERN TROUGH, WHICH EVENTUALLY RESULTS  
IN SOME PLACEMENT DIFFERENCES OF A DEEPENING LOW PRESSURE SYSTEM  
OFF THE NORTHEAST COAST. THE LATEST GFS IS STRONGER WITH THE  
SYSTEM, WHILE THE CMC IS FARTHEST SOUTH. BY DAY 5/MONDAY, THE GFS  
AND CMC ARE A LITTLE BIT STRONGER WITH A SHORTWAVE MOVING INTO THE  
PACIFIC NORTHWEST, WHICH EVENTUALLY PROPAGATES DOWNSTREAM INTO THE  
EASTERN TROUGH, AND OFFERS ADDITIONAL DIFFERENCES IN  
EVOLUTION/SHAPE OF THE EASTERN TROUGH LATE PERIOD. BY THAT POINT  
THOUGH, THERE'S ENOUGH RUN TO RUN VARIABILITY IN THE MODELS THAT  
LEANING MORE ON THE ENSEMBLE MEANS SEEMS TO BE THE BEST FOR NOW.  
 
THE WPC FORECAST USED A GENERAL DETERMINISTIC MODEL BLEND FOR DAYS  
3-5 AMIDST DECENT MODEL AGREEMENT. THEREAFTER, MORE WEIGHTING  
TOWARDS THE ENSEMBLE MEANS WERE USED TO HELP MITIGATE SOME OF THE  
SMALLER SCALE, HARD TO RESOLVE, DETAIL. DID MAINTAIN MODEST  
AMOUNTS OF THE ECMWF AND GFS JUST FOR SOME ADDED SYSTEM  
DEFINITION. THIS APPROACH MAINTAINS GOOD CONTINUITY WITH THE  
PREVIOUS WPC FORECAST FOR DAYS 3-6.  
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
WESTERLY FLOW ACROSS THE STILL RELATIVELY WARM GREAT LAKES ON  
SATURDAY SHOULD PROVIDE FAVORABLE CONDITIONS FOR LAKE EFFECT AND  
INTERIOR NORTHEAST (PARTICULARLY HIGHER ELEVATION) SNOW. MODERATE  
TO LOCALLY HEAVY SNOW AMOUNTS DOWNWIND OF LAKE ONTARIO, THE  
ADIRONDACKS, AND NORTHERN NEW ENGLAND ARE POSSIBLE. MEANWHILE, A  
PLUME OF MOISTURE/ATMOSPHERIC RIVER COMING INTO THE PACIFIC  
NORTHWEST COULD BRING 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 NORTHERN PARTS OF THE ROCKIES AS WELL THIS WEEKEND BUT  
QUICKLY DRY OUT EARLY NEXT WEEK. THEN ANOTHER ROUND OF  
PRECIPITATION IS FORECAST FOR THE PACIFIC NORTHWEST BY AROUND NEXT  
TUESDAY. 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 AND ENERGY ACROSS THE  
SOUTHERN PLAINS MAY BRING SOME LIGHT PRECIPITATION TO THESE  
REGIONS BUT NOTHING LOOKS PARTICULARLY IMPACTFUL AT THIS TIME.  
 
A BUILDING 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.  
 
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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