269  
FXUS02 KWBC 110642  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
141 AM EST TUE DEC 11 2018  
 
VALID 12Z FRI DEC 14 2018 - 12Z TUE DEC 18 2018  
   
..HEAVY PRECIPITATION THREAT FOR THE NORTHWEST
 
   
..HEAVY RAIN THREAT FOR THE LOWER MS VALLEY THROUGH THE EAST
 
 
   
..OVERVIEW AND GUIDANCE EVALUATION/PREFERENCES
 
 
IT REMAINS EVIDENT THAT THE WEATHER PATTERN FOR THE NEXT WEEK WILL  
REMAIN QUITE ACTIVE FROM THE NORTHWEST INTO CA AND BECOME  
INCREASINGLY WET FOR MUCH OF THE EASTERN HALF OF THE NATION LATE  
WEEK INTO THE WEEKEND. THERE REMAINS A STRONG GUIDANCE SIGNAL  
HERALDING THESE HAZARDS. DETERMINISTIC MODELS CONTINUE TO WAVER  
SIGNIFICANTLY OVER TIME WITH EMBEDDED SYSTEM DETAILS IN AN  
OTHERWISE RATHER PREDICTABLE LONGWAVE UPPER PATTERN EVOLUTION THAT  
SEEMS WELL REPRESENTED BY RECENT ENSEMBLE MEANS. ACCORDINGLY, THE  
WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY DERIVED FROM A  
COMPOSITE BLEND OF THE LATEST GEFS/ECMWF ENSEMBLE MEANS.  
 
   
..WEATHER HIGHLIGHTS AND HAZARDS
 
 
PRECIPITATION/WIND WILL SUBSTANTIALLY INCREASE FROM THE NORTHWEST  
INTO CA FRI INTO THE WEEKEND THEN AGAIN SUN-NEXT TUE WITH A  
SUCCESSION OF APPROACHING ENERGETIC PACIFIC SHORTWAVES/FRONTAL  
SYSTEMS. HIGHER PACIFIC NORTHWEST TERRAIN WILL SEE THE HEAVIEST  
RAIN/MOUNTAIN SNOW (WITH VARYING SNOW LEVELS AS TEMPERATURES RISE  
AND FALL BETWEEN EACH SYSTEM, WITH SNOWS THEN WORKING TO THE  
NORTH-CENTRAL GREAT BASIN/ROCKIES.  
 
LEAD SHORTWAVE ENERGY DIGGING INTO THE SOUTHERN PLAINS/LOWER MS  
VALLEY THU-FRI IS EXPECTED TO CARVE OUT A CLOSED LOW AND SPAWN  
SURFACE CYCLOGENESIS/FRONTOGENESIS. AMPLE GULF MOISTURE/WARM  
ADVECTION INCREASING AHEAD OF THE DEEPENING SYSTEM WILL EXPAND THE  
PRECIPITATION SHIELD TO THE EAST AND WRAPPING TO THE NORTH OF THE  
SURFACE LOW. RELATIVELY SLOW MOVEMENT OF THE WELL ORGANIZED SYSTEM  
AND FAVORABLE DYNAMICS SUPPORT A HEAVY RAIN THREAT FOR THE LOWER  
MS VALLEY/MID-SOUTH TO SOUTHEAST. HEAVY RAINFALL WILL ROBUSTLY  
SPREAD THROUGH THE APPALACHIANS AND EASTERN SEABOARD WITH ADDED  
INFUSION OF ATLANTIC MOISTURE. RUNOFF PROBLEMS WILL BE ENHANCED IN  
AREAS WITH RECENT HEAVY SNOWFALL. HEAVY SNOWS MAY ALSO WRAP INTO A  
MARGINALLY COOLED MIDWEST/GREAT LAKES TO INTERIOR NORTHEAST  
AIRMASS.  
 
SCHICHTEL  
 
WPC MEDIUM RANGE 500 MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, WINTER WEATHER OUTLOOK PROBABILITIES  
AND HEAT INDEXES ARE FOUND 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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