567  
FXUS02 KWBC 010700  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
159 AM EST WED DEC 1 2021  
 
VALID 12Z SAT DEC 4 2021 - 12Z WED DEC 8 2021  
   
..OVERVIEW
 
 
A QUASI-ZONAL FLOW PATTERN IS EXPECTED TO BE IN PLACE TO BEGIN THE  
WEEKEND ACROSS THE NORTHERN TIER STATES WITH A BROAD TROUGH OVER  
THE GREAT LAKES AND NORTHEAST, AND AN UPPER RIDGE OVER THE  
INTERMOUNTAIN WEST WITH AN UPPER LOW SOUTHWEST OF CALIFORNIA.  
THERE WILL LIKELY BE TWO ORGANIZED STORM SYSTEMS TO CONTEND WITH  
THROUGH THE MIDDLE OF NEXT WEEK, WITH THE FIRST TRACKING FROM THE  
MIDWEST TO THE NORTHEAST THROUGH MONDAY, AND THE SECOND ONE  
TRACKING FROM THE CENTRAL ROCKIES TO THE OHIO VALLEY AND MID-SOUTH  
BY WEDNESDAY.  
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
THE 00Z MODEL GUIDANCE SUITE IS IN DECENT AGREEMENT ON SATURDAY  
BEFORE MORE NOTICEABLE DIFFERENCES EMERGE BY MONDAY, WITH THE GFS  
INDICATING A FASTER SHORTWAVE PASSING THROUGH THE PACIFIC  
NORTHWEST COMPARED TO THE MODEL CONSENSUS, AND SLIGHTLY MORE  
AMPLIFIED WITH THE TROUGH OVER THE GREAT LAKES. BY THE END OF THE  
FORECAST PERIOD, THERE IS A BIT OF MODEL SPREAD WITH THE UPPER LOW  
OVER NORTHWESTERN MEXICO, BUT THIS IS NOT EXPECTED TO BE IMPACTFUL  
IN TERMS OF SENSIBLE WEATHER. THERE ARE STILL TIMING AND  
AMPLITUDE DIFFERENCES WITH THE SECOND STORM SYSTEM CROSSING THE  
CENTRAL U.S. BY THE MIDDLE OF THE WEEK, AND THE ENSEMBLE MEANS  
PROVIDED A GOOD STARTING POINT FOR PLACEMENT.  
 
THE WPC FORECAST WAS PRIMARILY BASED ON A CMC/ECMWF/GFS BLEND  
THROUGH SUNDAY. THEREAFTER, INCREASED WEIGHTING TOWARDS THE  
ENSEMBLE MEANS WHILST KEEPING SOME OF THE OPERATIONAL GFS AND  
ECMWF AND SOME PREVIOUS WPC CONTINUITY.  
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
ROUNDS OF LIGHT TO MODERATE PRECIPITATION ARE FORECAST FOR THE  
MIDWEST, GREAT LAKES, AND NORTHEAST WITH A PROGRESSIVE STORM TRACK  
OVER THE REGION THROUGH MONDAY, WITH SNOW EXPECTED TO BE THE MAIN  
PRECIP TYPE OVER THE NORTHERN GREAT LAKES AND NORTHERN NEW  
ENGLAND. MOISTURE INCREASING AHEAD OF THE COLD FRONT IS EXPECTED  
TO RESULT IN SCATTERED SHOWERS AND A FEW THUNDERSTORMS FROM THE  
DEEP SOUTH TO THE OHIO VALLEY OVER THE WEEKEND, BUT AMOUNTS ARE  
NOT CURRENTLY EXPECTED TO BE EXCESSIVE. A SHORTWAVE AND COLD  
FRONT REACHING THE PACIFIC NORTHWEST BY SUNDAY NIGHT AND THROUGH  
MONDAY IS EXPECTED TO RESULT IN ANOTHER ROUND OF MODERATE TO  
LOCALLY HEAVY RAIN AND MOUNTAIN SNOWS TO WESTERN WASHINGTON AND  
OREGON, WITH SOME OF THIS MOISTURE REACHING THE NORTHERN ROCKIES  
BY TUESDAY WITH HEAVY SNOW POSSIBLE FOR THE HIGHER ELEVATIONS OF  
NORTHERN IDAHO, WESTERN MONTANA, AND WESTERN WYOMING. BY THE END  
OF THE FORECAST PERIOD NEXT WEDNESDAY, ADDITIONAL SHOWERS AND SOME  
STORMS ARE LIKELY TO DEVELOP AHEAD OF A SECOND COLD FRONT CROSSING  
THE MISSISSIPPI RIVER VALLEY.  
 
TEMPERATURES ARE EXPECTED TO BE ABOVE NORMAL FOR EARLY DECEMBER  
ACROSS MOST OF THE NATION THROUGH EARLY NEXT WEEK, WITH THE  
GREATEST POSITIVE ANOMALIES EXPECTED FOR WESTERN HIGH PLAINS ON  
SATURDAY WHERE HIGHS ARE FORECAST TO BE 15 TO 20 DEGREES ABOVE  
AVERAGE. ANOTHER EPISODE OF WELL ABOVE NORMAL TEMPERATURES IS  
LIKELY FOR PARTS OF TEXAS AND OKLAHOMA ON TUESDAY AHEAD OF THE  
NEXT COLD FRONT. ON THE OTHER END OF THE SPECTRUM, COLD WEATHER  
IS FORECAST TO CONTINUE ACROSS THE NORTHEAST U.S. WITH HIGHS  
RUNNING UP TO 10 DEGREES BELOW NORMAL THROUGH THE WEEKEND WITH A  
COLD UPPER LEVEL TROUGH OVERHEAD. HOWEVER, NO MAJOR ARCTIC  
AIRMASS INTRUSIONS ARE EXPECTED DURING THIS FORECAST PERIOD.  
 
HAMRICK  
 
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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