487  
FXUS02 KWBC 271901  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
200 PM EST SAT NOV 27 2021  
 
VALID 12Z TUE NOV 30 2021 - 12Z SAT DEC 04 2021  
   
..OVERVIEW
 
 
PERIODS OF RELATIVELY LOW AMPLITUDE UPPER TROUGHING ARE EXPECTED  
FOR PARTS OF THE CENTRAL AND EASTERN U.S. AS SHORTWAVES MOVE  
QUICKLY THROUGH THE MEAN FLOW, AND THESE IMPULSES COULD LEAD TO  
LIGHT PRECIPITATION FROM THE MIDWEST TO NORTHEAST, ESPECIALLY FOR  
FAVORED LAKE EFFECT AND TERRAIN AREAS. MEANWHILE IN THE  
WESTERN/CENTRAL U.S., UPPER RIDGING WILL BE IN PLACE FOR MUCH OF  
THE PERIOD, CAUSING MILDER THAN AVERAGE TEMPERATURES WITH  
POTENTIALLY RECORD-BREAKING WARMTH.  
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
THE 00Z/06Z MODEL GUIDANCE BEGINS THE MEDIUM RANGE PERIOD TUESDAY  
WITH REASONABLY GOOD AGREEMENT WITH THE OVERALL PATTERN, THOUGH  
SLIGHT DIFFERENCES REMAIN WITH SHORTWAVES TRACKING THROUGH  
SOUTHERN CANADA AND THE GREAT LAKES EVEN EARLY IN THE PERIOD. BUT  
THE GENERAL CONSENSUS IS FOR SHORTWAVE ENERGY TO QUICKLY DIG  
THROUGH THE CENTRAL AND EASTERN U.S. WEDNESDAY INTO THURSDAY,  
WHILE ADDITIONAL ENERGY AND A SURFACE LOW TRACK CANADA AND INTO  
THE GREAT LAKES REGION BY THURSDAY. MEANWHILE THERE ARE MINIMAL  
DIFFERENCES REGARDING RIDGING IN THE WEST, AND SOUTHERN STREAM  
COMPACT LOWS IN THE EASTERN PACIFIC THAT SHOW SOME PLACEMENT AND  
STRENGTH DIFFERENCES MAY NOT HAVE MUCH OF AN EFFECT ON THE CONUS.  
A MULTI-MODEL DETERMINISTIC BLEND OF THE 00Z ECMWF, CMC, AND UKMET  
AND 06Z GFS WAS UTILIZED EARLY IN THE PERIOD AS GUIDANCE WAS  
FAIRLY WELL CLUSTERED.  
 
GREATER MODEL DIFFERENCES ARISE LATER THURSDAY AND THROUGH THE END  
OF THE WEEK AS SHORTWAVE ENERGY STEMMING FROM THE LOWER  
PREDICTABILITY HIGHER LATITUDES AND/OR OVER THE PACIFIC TRACK INTO  
AND ACROSS THE U.S. AND CANADA. AT THIS FORECAST LEAD TIME IT IS  
DIFFICULT TO TELL HOW THESE RELATIVELY SMALL AND LOW  
PREDICTABILITY FEATURES WILL EVOLVE, AND DETERMINISTIC GUIDANCE  
AND ENSEMBLE MEMBERS VARY GREATLY WITH WHICH SHORTWAVES BECOME THE  
ONES TO DIG CONSIDERABLY AND CREATE MEANINGFUL CHANGES TO THE  
LARGE SCALE FLOW. RUN TO RUN VARIABILITY REMAINS HIGH PARTICULARLY  
WITH THE DETERMINISTIC ECMWF RUNS, BUT THE GFS RUNS DO NOT  
NECESSARILY AGREE WITH THE ENSEMBLE MEANS EITHER. FOR THE LATTER  
PART OF THE MEDIUM RANGE PERIOD, TRENDED QUICKLY TOWARD A GEFS AND  
EC ENSEMBLE MEAN BLEND, SINCE THESE WERE BETTER ALIGNED WITH EACH  
OTHER AND LESSENED INDIVIDUAL MODEL DIFFERENCES. THE MAIN CHANGE  
TO THE PREVIOUS FORECAST WAS TO TRACK FRONTS SOMEWHAT FASTER  
ACROSS THE CENTRAL AND EASTERN U.S. PER THE UNCERTAIN BUT OVERALL  
MODEL CONSENSUS. THIS ALSO LOWERED EXPECTED QPF ACROSS THE  
MID-SOUTH WITH SHORTER RESONANCE TIME OF THE FRONT.  
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
AS ROUNDS OF SHORTWAVE ENERGY PASS OVER THE NORTH-CENTRAL TO  
NORTHEASTERN U.S., EXPECT GENERALLY LIGHT PRECIPITATION ACROSS  
THOSE AREAS. WITH THE WEST AND NORTHWESTERLY FLOW, FAVORED LAKE  
ENHANCEMENT AREAS AS WELL AS UPSLOPE TERRAIN IN THE INTERIOR  
NORTHEAST COULD SEE ENHANCED TOTALS, AND AT THIS TIME IT APPEARS  
DOWNWIND OF LAKE ONTARIO INTO THE ADIRONDACKS SHOULD SEE THE  
HIGHEST PRECIPITATION AMOUNTS. MEANWHILE, PERIODS OF MOIST ONSHORE  
FLOW INTO THE OLYMPIC PENINSULA AND THE NORTHERN CASCADES SHOULD  
LEAD TO GENERALLY MODERATE RAIN AND SNOW AMOUNTS, ESPECIALLY  
TUESDAY INTO WEDNESDAY. SNOW LEVELS ARE UNCERTAIN AT THIS POINT  
WITH THE RIDGIER GFS SUITE SHOWING RAIN AND LESS PRECIPITATION  
REACHING INTO WASHINGTON, WHILE THE EC AND CMC ARE WETTER AND HAVE  
LOWER SNOW LEVELS, BUT AT LEAST THE HIGHEST TERRAIN SHOULD HAVE  
SNOW. NORTHERN PARTS OF THE ROCKIES WILL ALSO SEE LIGHT TO  
MODERATE PRECIPITATION IN THIS PATTERN. OTHER THAN THESE TWO  
HIGHLIGHTED REGIONS, A MAJORITY OF THE COUNTRY WILL BE GENERALLY  
DRY OTHER THAN INCREASING MOISTURE FOR THE LATTER PART OF THE WEEK  
FROM SOUTHERN TEXAS NORTHEASTWARD INTO THE MID-SOUTH.  
 
TEMPERATURES ARE EXPECTED TO BE CONSIDERABLY ABOVE NORMAL FOR MUCH  
OF THE COUNTRY NEXT WEEK THANKS TO RIDGING OVERHEAD. BOTH HIGHS  
AND LOWS ARE FORECAST TO BE 20-30 DEGREES ABOVE AVERAGE FOR  
NORTHERN AND CENTRAL PORTIONS OF THE HIGH PLAINS AND EXPANDING  
INTO THE MISSISSIPPI VALLEY WEDNESDAY AND THURSDAY. A FEW  
LOCATIONS MAY REACH OR EXCEED DAILY MAXIMUM AND MINIMUM  
TEMPERATURE RECORDS WITH THESE MILD TEMPERATURES. AS THE FLOW  
FLATTENS DURING THE LATE PERIOD, ABOVE NORMAL TEMPERATURES SHOULD  
SPREAD TOWARD THE EAST COAST FOR THE LATTER PART OF THE WORKWEEK  
AFTER A COOLER THAN AVERAGE START.  
 
TATE  
 
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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