990  
FXUS02 KWBC 120653  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
152 AM EST SUN DEC 12 2021  
 
VALID 12Z WED DEC 15 2021 - 12Z SUN DEC 19 2021  
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
GUIDANCE CLUSTERING AND FORECAST SPREAD/PREDICTABILITY THROUGH  
MEDIUM RANGE REMAINS MUCH BETTER THAN NORMAL. THE WPC MEDIUM RANGE  
PRODUCT SUITE WAS PRIMARILY DERIVED FROM A COMPOSITE OF THE 18 UTC  
GFS AND 12 UTC ECMWF/CANADIAN ALONG WITH THE 01 UTC NATIONAL BLEND  
OF MODELS DAYS 3-7. THIS BLEND YIELDED A SOLUTION QUITE COMPATIBLE  
WITH THE PREVIOUS WPC FORECAST PACKAGE AND SEEMS WELL SUPPORTED BY  
GEFS/NAEFS/ECMWF ENSEMBLES. LATEST 00 UTC GUIDANCE OVERALL REMAINS  
CONSISTENT WITH THIS COMPOSITE THROUGH MUCH OF THE FORECAST  
PERIOD.  
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
A VIGOROUS UPPER TROUGH WILL LIFT NORTHEASTWARD FROM THE SOUTHWEST  
MIDWEEK, BRINGING WIDESPREAD MOUNTAIN SNOW/RAIN THROUGH THE GREAT  
BASIN AND NORTHERN/CENTRAL ROCKIES. AS THE SYSTEM LIFTS THROUGH  
THE PLAINS WED-THU, RAPID CYCLOGENESIS ACROSS THE NORTH-CENTRAL  
U.S. WILL LEAD TO AN EXPANSIVE AREA OF STRONG WINDS, TOGETHER WITH  
A SWATH OF WINTRY PRECIPITATION THROUGH THE NORTH SIDE OF THE LOW  
TRACK ACROSS THE NORTHERN PLAINS AND UPPER MIDWEST TO THE UPPER  
GREAT LAKES. AHEAD OF THE DEEP CYCLONE, AN UPPER RIDGE WILL BUILD  
OVER THE CENTRAL U.S. WHERE ANOMALOUS WARMTH WILL BE MOST  
PRONOUNCED MIDWEEK WITH RECORD HIGH TEMPERATURES UPWARDS TO 30-40F  
ABOVE NORMAL. MODEST LEAD RAINS THAT SHOULD FALL ON TOP OF RECENT  
UPPER MIDWEST SNOWS TOGETHER WITH THE RECORD WARMTH COULD LEAD TO  
FLOODING ISSUES. ANOMALOUS WARMTH AHEAD OF THE TRAILING COLD  
FRONT, WITH POSITIVE ANOMALIES UPWARDS TO 15-25F, WILL REACH THE  
EAST LATE WEEK. THE MODERATING FRONT WILL STALL ACROSS THE DEEP  
SOUTH. AN AXIS OF ENHANCED RAINFALL IS FORECAST TO SET UP FROM THE  
SOUTHERN PLAINS THROUGH THE MID-SOUTH AND THE OH VALLEY/NORTHEAST  
FRI/NEXT WEEKEND WITH EMERGING RETURN FLOW AND ORGANIZED FRONTAL  
WAVE DEVELOPMENT AND LIFT. A SWATH OF WEEKEND SNOW MAY ALSO OCCUR  
ON THE COOLED NORTHWEST PERIPHERY OF THIS PRECIPITATION SHIELD.  
 
UPSTREAM ON THE HEELS OF THE AFOREMENTIONED LEAD STORM, ANOTHER  
MOISTURE SURGE AND MODERATE TO HEAVY PRECIPITATION IS FORECAST TO  
REACH NORTHERN CALIFORNIA AND OREGON WED/THU AS THE NEXT PACIFIC  
CYCLONE REACHES THE WEST COAST. GUIDANCE SIGNAL IS ALSO GROWING  
THAT MOISTURE FROM YET ANOTHER PACIFIC SYSTEM WILL MODESTLY IMPACT  
THE PACIFIC NORTHWEST NEXT WEEKEND.  
 
SCHICHTEL  
 
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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