491  
FXUS02 KWBC 020650  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
150 AM EST THU DEC 2 2021  
 
VALID 12Z SUN DEC 5 2021 - 12Z THU DEC 9 2021  
   
..OVERVIEW
 
 
THE OVERALL UPPER LEVEL PATTERN IS FORECAST TO TRANSITION FROM  
QUASI-ZONAL TO MORE AMPLIFIED, WITH THE WESTERN U.S. UPPER RIDGE  
BECOMING ESTABLISHED FARTHER WEST OVER THE EASTERN PACIFIC AND  
MULTIPLE TROUGHS PASSING OVER THE PLAINS AND MIDWEST. 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 LATE MONDAY, AND THE SECOND ONE TRACKING  
FROM THE CENTRAL ROCKIES TO THE OHIO VALLEY AND MID-SOUTH BY  
MIDWEEK. AN ALBERTA CLIPPER-TYPE SYSTEM MAY AFFECT THE NORTHERN  
PLAINS BY NEXT THURSDAY.  
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
THERE HAS BEEN AN OVERALL IMPROVEMENT IN THE CONSOLIDATION OF THE  
00Z MODEL GUIDANCE COMPARED TO RECENT DAYS AS THE OVERALL PATTERN  
BECOMES MORE AMPLIFIED, WITH FORECAST CONFIDENCE NOW AVERAGE  
COMPARED TO BELOW AVERAGE IN RECENT DAYS. WITH THE FIRST STORM  
SYSTEM CROSSING THE GREAT LAKES/NORTHEAST THROUGH MONDAY, THE GFS  
WAS FASTER AND FARTHER NORTH THAN THE MODEL CONSENSUS, INCLUDING  
ITS OWN ENSEMBLE MEAN, SO IT WAS NOT FAVORED THROUGH EARLY  
TUESDAY.  
 
THE CHARACTER OF THE NEXT SHORTWAVE NEARING THE NORTHWEST EARLY  
NEXT WEEK WILL DEPEND ON HOW MUCH IF ANY INTERACTION THERE MAY BE  
BETWEEN NORTHERN STREAM ENERGY JUST SOUTH OF ALASKA AND A SEPARATE  
UPPER LOW FARTHER SOUTH, WITH NO CLEAR CONSENSUS EVIDENT YET FOR  
EXACTLY WHAT WILL HAPPEN. THIS LEADS TO NOTEWORTHY MODEL  
DIFFERENCES, WITH THE GFS INITIALLY QUITE STRONG WITH THE  
SHORTWAVE AND FASTER, AND THE CMC IS CONSIDERABLY SLOWER AND  
FARTHER WEST, AND A GOOD DEAL OF SPREAD AMONG INDIVIDUAL ENSEMBLE  
MEMBERS. THE CMC IS ALSO FARTHER EAST THAN THE CONSENSUS WITH THE  
UPPER LOW NEAR NORTHWEST MEXICO, BUT THIS DOES NOT APPEAR TO HAVE  
A SIGNIFICANT IMPACT ON SENSIBLE WEATHER AT THIS TIME.  
 
THE FIRST HALF OF THE FORECAST INCORPORATED THE ECMWF/CMC/UKMET  
AND SOME OF THE ECENS, WITH THE GFS EXCLUDED DUE TO THE REASONS  
PREVIOUSLY MENTIONED. HOWEVER, THE GFS WAS SLIGHTLY MORE IN LINE  
WITH THE OVERALL PATTERN BY LATE IN THE PERIOD, SO IT WAS  
SUBSTITUTED FOR THE CMC ALONG WITH MORE OF THE ENSEMBLE MEANS.  
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
THERE IS THE POTENTIAL FOR A BAND OF LIGHT TO MODERATE SNOW FROM  
NORTHERN MICHIGAN TO NORTHERN NEW ENGLAND THROUGH MONDAY AS AN  
ORGANIZED STORM SYSTEM PASSES THROUGH THE REGION. PRECIPITATION  
TYPE AND INTENSITY OVER THE EASTERN GREAT LAKES AND NEW ENGLAND  
WILL DEPEND ON THE EXACT LOW TRACK. 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 THROUGH  
MONDAY MORNING. THERE COULD BE SOME LOCALLY MODERATE TO HEAVY  
RAIN EMBEDDED WITHIN THIS AREA BUT WITH FAIRLY LOW CONFIDENCE  
REGARDING EXACT PLACEMENT.  
 
THE SHORTWAVE AND COLD FRONT FORECAST TO REACH THE PACIFIC  
NORTHWEST BY SUNDAY NIGHT AND THROUGH MONDAY SHOULD PRODUCE A  
PERIOD OF MODERATE TO LOCALLY HEAVY RAIN AND MOUNTAIN SNOWS OVER  
WESTERN WASHINGTON AND OREGON, WITH SOME OF THIS MOISTURE REACHING  
THE NORTHERN ROCKIES BY TUESDAY. HEAVY SNOW WILL BE POSSIBLE FOR  
THE HIGHER ELEVATIONS OF NORTHERN IDAHO, WESTERN MONTANA, AND  
WESTERN WYOMING. IN ADDITION, SOME MOISTURE WILL LIKELY EXTEND  
FARTHER SOUTH OVER FAVORED TERRAIN IN THE GREAT BASIN AND CENTRAL  
ROCKIES. BY THE WEDNESDAY-THURSDAY TIME PERIOD, MORE RAINFALL IS  
LIKELY FOR THE EAST-CENTRAL U.S. AHEAD OF THIS SAME STORM SYSTEM,  
AND WINTRY PRECIPITATION FARTHER NORTH ACROSS THE GREAT LAKES AND  
NEW ENGLAND.  
 
TEMPERATURES ARE EXPECTED TO BE NEAR TO ABOVE NORMAL FOR EARLY  
DECEMBER ACROSS MOST OF THE NATION THROUGH THE EARLY TO MIDDLE OF  
NEXT WEEK, WITH THE GREATEST POSITIVE ANOMALIES EXPECTED FOR  
WESTERN PORTIONS 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, AND ANOTHER ROUND OF BELOW  
AVERAGE READINGS ON TUESDAY ALONG THE EAST COAST WHICH SHOULD  
MODERATE BY WEDNESDAY. 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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