031  
FXUS02 KWBC 111901  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
200 PM EST SAT DEC 11 2021  
 
VALID 12Z TUE DEC 14 2021 - 12Z SAT DEC 18 2021  
 
...ANOTHER MOISTURE SURGE IS FORECAST TO REACH NORTHERN CALIFORNIA  
AND OREGON MIDWEEK AS HEAVY PRECIPITATION WINDS DOWN IN SOUTHERN  
CALIFORNIA...  
 
...RECORD WARMTH TO SPREAD FROM THE CENTRAL U.S. TOWARD THE  
SNOW-COVERED REGION OF UPPER MIDWEST AHEAD OF AN INTENSIFYING  
CYCLONE...  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
MODEL AND ENSEMBLE FORECAST CLUSTERING AND SPREAD THROUGH MOST OF  
THE MEDIUM RANGE REMAINS MUCH BETTER THAN NORMAL, BOLSTERING  
FORECAST CONFIDENCE. THE WPC MEDIUM RANGE FORECAST PACKAGE WAS  
BASED ON 40% FROM THE 06Z GFS AND GEFS, 40% FROM THE 00Z ECMWF/EC  
MEAN, AND 20% FROM THE 00Z CMC/CMC MEAN. MORE WEIGHTS FROM THE  
ENSEMBLE MEANS WERE APPLIED STARTING FROM DAY 5.5. THIS BLEND  
YIELDED A SOLUTION QUITE COMPATIBLE WITH THE PREVIOUS WPC FORECAST  
PACKAGE.  
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
AN AMPLIFIED UPPER TROUGH WILL PUSH ONSHORE INTO THE SOUTHWEST  
NEXT TUESDAY INTO WEDNESDAY. WIDESPREAD TERRAIN-ENHANCED RAINFALL  
AND HEAVY MOUNTAIN SNOWS OVER SOUTHERN CALIFORNIA ON TUESDAY WILL  
LIKELY WIND DOWN BY WEDNESDAY AS THE TROUGH PUSHES INLAND AND THEN  
LIFT NORTHEASTWARD THROUGH THE WESTERN U.S. MIDWEEK, BRINGING  
WIDESPREAD MOUNTAIN SNOW/RAIN THROUGH THE GREAT BASIN AND  
NORTHERN/CENTRAL ROCKIES. AS THE MAIN SYSTEM LIFTS NORTHEASTWARD  
THROUGH THE PLAINS NEXT WED-THU, THE POSSIBILITY OF RAPID  
CYCLOGENESIS ACROSS THE NORTHERN U.S. WILL LIKELY 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 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 ACROSS THE CENTRAL  
U.S. IN FACT, RECORD HIGH TEMPERATURES UPWARDS TO 40F ABOVE  
NORMAL NEXT WEDNESDAY WILL LIKELY SPREAD TOWARD A REGION OF THE  
UPPER MIDWEST WHERE SIGNIFICANT AMOUNTS OF SNOW JUST FELL  
RECENTLY. ANY RAIN THAT SHOULD FALL ON TOP OF THE SNOW TOGETHER  
WITH THE RECORD WARMTH COULD LEAD TO FLOODING ISSUES.  
 
BEHIND THE AMPLIFIED UPPER TROUGH, ANOTHER MOISTURE SURGE IS  
FORECAST TO REACH NORTHERN CALIFORNIA AND OREGON MIDWEEK AS THE  
NEXT PACIFIC CYCLONE APPROACHES THE WEST COAST. MODERATE TO HEAVY  
PRECIPITATION SHOULD CONTINUE ACROSS THESE AREAS THROUGH MIDWEEK.  
IT APPEARS THAT MOISTURE FROM THE NEXT PACIFIC SYSTEM WILL IMPACT  
THE PACIFIC NORTHWEST ON FRIDAY AND INTO THE WEEKEND.  
 
ON THE EAST COAST, ANOMALOUS WARMTH AHEAD OF A COLD FRONT WILL  
REACH THE AREA LATE NEXT WEEK. MEANWHILE, THE TRAILING PORTION OF  
THE COLD FRONT WILL LIKELY BECOME NEARLY STATIONARY ACROSS THE  
DEEP SOUTH WHERE AN AXIS OF ENHANCED RAINFALL IS FORECAST TO SET  
UP ACROSS THE SOUTHERN PLAINS THROUGH THE TENNESSEE VALLEY.  
 
KONG  
 
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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