686  
FXUS02 KWBC 090507  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1207 AM EST SUN DEC 09 2018  
 
VALID 12Z WED DEC 12 2018 - 12Z SUN DEC 16 2018  
 
...HEAVY RAIN/WRAPPED SNOW THREAT INTO PARTS OF THE EASTERN U.S.  
LATE WEEK...  
 
   
..OVERVIEW AND GUIDANCE EVALUATION/PREFERENCES
 
 
THE WEATHER PATTERN THIS WEEK IS EXPECTED TO REMAIN QUITE ACTIVE  
ACROSS THE NORTHWEST AND BECOME INCREASINGLY WET FOR MUCH OF THE  
EASTERN THIRD OF THE NATION LATER WEEK. THE MODELS CONTINUE TO  
WAVER IN THE DETAILS IN AN OTHERWISE RATHER PREDICTABLE LONGWAVE  
UPPER PATTERN THAT IS WELL-REPRESENTED IN THE LATEST ENSEMBLE  
MEANS. ACCORDINGLY, THE WPC MEDIUM RANGE PRODUCT SUITE WAS  
PRIMARILY DERIVED FROM A COMPOSITE BLEND OF THE COMPATABLE LATEST  
GEFS/ECMWF ENSEMBLE MEANS AND CONTINUITY, WITH MODEST WEIGHTING  
APPLIED TO THE LATEST GFS/ECMWF.  
 
   
..WEATHER HIGHLIGHTS AND HAZARDS
 
 
PRECIPITATION/WIND PERIODICALLY INCREASES INTO THE NORTHWEST  
MIDWEEK AND AGAIN INTO NEXT WEEKEND AS HEIGHTS FALL WITH A  
SUCCESSION OF APPROACHING SHORTWAVES/FRONTAL SYSTEMS. HIGHER  
PACIFIC NORTHWEST TERRAIN WILL OBSERVE THE HEAVIEST RAIN/MOUNTAIN  
SNOW, WITH ACTIVITY THEN WORKING TO THE NORTH-CENTRAL GREAT  
BASIN/ROCKIES WITH SYSTEM ADVANCE.  
 
BY THURSDAY, LEAD PACIFIC SHORTWAVE ENERGY DIVES FROM THE ROCKIES  
TO THE SOUTHERN PLAINS TO REINFORCE UPPER TROUGHING WHILE SPAWNING  
SURFACE CYCLOGENESIS. GULF MOISTURE/WARM ADVECTION INCREASING  
AHEAD OF THE DEEPENING SYSTEM HELPS TO EXPAND THE PRECIPITATION  
SHIELD TO THE EAST AND WRAPPED AROUND TO THE NORTH OF THE SURFACE  
LOW. RELATIVELY SLOW MOVEMENT OF THE SYSTEM WILL SUPPORT A HEAVY  
RAIN THREAT AND COLD SECTOR SNOWS THROUGH THE MIDWEST/GREAT LAKES  
AND INTERIOR MID-ATLANTIC/NORTHEAST MAINLY TO THE NORTHWEST OF THE  
UNCERTAIN LOW TRACK. RAINFALL MAY BE HEAVY FROM THE EAST SIDE OF  
THE APPALACHIANS TO THE COASTAL PLAIN WITH THE INFUSION OF  
ATLANTIC MOISTURE AS WELL, WHICH MAY FALL OVER AREAS RECEIVING  
APPRECIABLE WEEKEND SNOWFALLS, ESPECIALLY OVER THE SOUTHERN  
APPALACHIANS.  
 
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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