621  
FXUS02 KWBC 100645  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
144 AM EST MON DEC 10 2018  
 
VALID 12Z THU DEC 13 2018 - 12Z MON DEC 17 2018  
   
..HEAVY PRECIPITATION THREAT FOR THE NORTHWEST
 
   
..HEAVY RAIN THREAT FOR THE LOWER MS VALLEY THROUGH THE EAST
 
 
...HEAVY SNOW THREAT MID-MS/OH VALLEY THROUGH THE INTERIOR  
NORTHEAST...  
 
   
..OVERVIEW AND GUIDANCE EVALUATION/PREFERENCES
 
 
THE WEATHER PATTERN FOR THE NEXT WEEK WILL REMAIN QUITE ACTIVE  
OVER THE NORTHWEST INTO CA AND BECOME INCREASINGLY WET FOR MUCH OF  
THE EASTERN THIRD OF THE NATION LATER IN THE WEEK. THERE IS A  
STRONG GUIDANCE SIGNAL HERALDING THESE HAZARDS. HOWEVER,  
DETERMINISTIC MODELS CONTINUE TO WAVER INCREASINGLY OVER TIME  
(OFTEN SIGNIFICANTLY) WITH THE DETAILS IN AN OTHERWISE RATHER  
PREDICTABLE LONGWAVE UPPER PATTERN THAT IS WELL REPRESENTED FOR  
MUCH OF THE UPCOMING WEEK BY RECENT ENSEMBLE MEANS AND WPC  
CONTINUITY. ACCORDINGLY, THE WPC MEDIUM RANGE PRODUCT SUITE WAS  
PRIMARILY DERIVED FROM A COMPOSITE BLEND OF THE LATEST GEFS/ECMWF  
ENSEMBLE MEANS AND TO A LESSER EXTENT OVER TIME THE LATEST  
GFS/ECMWF.  
 
   
..WEATHER HIGHLIGHTS AND HAZARDS
 
 
PRECIPITATION/WIND WILL SUBSTANTIALLY INCREASE INTO THE NORTHWEST  
INTO CA FRI/SAT AND AGAIN BY MON/TUE AS HEIGHTS FALL WITH A  
SUCCESSION OF APPROACHING ENERGETIC PACIFIC SHORTWAVES/FRONTAL  
SYSTEMS. HIGHER PACIFIC NORTHWEST TERRAIN WILL OBSERVE THE  
HEAVIEST RAIN/MOUNTAIN SNOW (WITH VARYING SNOW LEVELS AS UPPER  
TEMPERATURES RISE AND FALL BETWEEN EACH SYSTEM), WITH ACTIVITY  
THEN WORKING TO THE NORTH-CENTRAL GREAT BASIN/ROCKIES.  
 
LEAD SHORTWAVE ENERGY DIGS FROM THE ROCKIES TO THE SOUTHERN PLAINS  
THU TO REINFORCE UPPER TROUGHING IN AN EMERGING SOUTHERN STREAM TO  
SPAWN SURFACE CYCLOGENESIS/FRONTOGENESIS. AMPLE GULF MOISTURE/WARM  
ADVECTION INCREASING AHEAD OF THE DEEPENING SYSTEM WILL HELP TO  
EXPAND THE PRECIPITATION SHIELD TO THE EAST AND ALSO WRAP TO THE  
NORTH OF THE SURFACE LOW. RELATIVELY SLOW MOVEMENT OF THE  
ORGANIZED SYSTEM AND FAVORABLE DYNAMICS SUPPORT A HEAVY RAIN  
THREAT FOR THE LOWER MS VALLEY/MID-SOUTH TO SOUTHEAST. HEAVY  
RAINFALL SPREADS TO THE EAST SIDE OF THE APPALACHIANS AND COASTAL  
PLAIN WITH ADDED INFUSION OF ATLANTIC MOISTURE. RUNOFF PROBLEMS  
WILL BE ENHANCED FOR AREAS WITH RECENT HEAVY SNOWFALL IN A LEAD-IN  
PATTERN WITH MODERATING TEMPERATURES. NEW HEAVY COLD SECTOR SNOWS  
ARE MEANWHILE LIKELY TO WRAP BACK INTO THE MIDWEST/GREAT  
LAKES/APPALACHIANS TO THE NORTHWEST OF THE UNCERTAIN LOW TRACK.  
 
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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