307  
FXUS02 KWBC 111554  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1053 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 EAST
 
 
   
..OVERVIEW AND GUIDANCE EVALUATION/PREFERENCES
 
 
AN INCREASINGLY STRONG SIGNAL FOR WIDESPREAD PRECIPITATION  
(HEAVIER PERIODS) FOR THE PACIFIC NORTHWEST, PORTIONS OF  
CALIFORNIA AND ACROSS THE SOUTHEAST/APPALACHIAN/MID-ATLANTIC  
REGION THROUGH THE EXTENDED FORECAST. SIGNIFICANT TIMING, LOCATION  
AND DEPTH DIFFERENCES AMONGST THE DETERMINISTIC AND ENSEMBLE  
GUIDANCE CONTINUED WITH THE LATEST GUIDANCE, THUS RESULTED IN  
BELOW AVERAGE CONFIDENCE FOR THIS FORECAST ISSUANCE. WPC MEDIUM  
RANGE PRODUCT SUITE WAS PRIMARILY DERIVED FROM A COMPOSITE BLEND  
OF THE LATEST GEFS/ECMWF ENSEMBLE MEANS WITH ABOUT 10% EACH OF THE  
00Z GFSP/ECWMF.  
 
   
..WEATHER HIGHLIGHTS AND HAZARDS
 
 
PRECIPITATION/WIND WILL SUBSTANTIALLY INCREASE FROM COASTAL  
WASHINGTON TO NORTHERN CALIFORNIA THROUGH THE WEEKEND AND INTO THE  
MIDDLE OF THE WEEK AS A SUCCESSION OF APPROACHING ENERGETIC  
PACIFIC SHORTWAVES/FRONTAL SYSTEMS PASS THROUGH THE REGION. 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. FORECAST PRECIPITATION UP TO 2 INCHES IS  
ANTICIPATED PRIMARILY FOR COASTAL AREAS- WITH ADDITIONAL 2 TO 5  
INCHES FORECAST BY THE 18TH.  
 
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 PORTION OF  
THE LOWER MS VALLEY/MID-SOUTH TO SOUTHEAST/MID-ATLANTIC. 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 AND ONGOING  
RIVER FLOODING. HEAVY SNOWS MAY ALSO WRAP INTO A MARGINALLY COOLED  
MIDWEST/GREAT LAKES TO INTERIOR NORTHEAST AIRMASS.  
 
CAMPBELL/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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