513  
FXUS02 KWBC 130556  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1256 AM EST THU DEC 13 2018  
 
VALID 12Z SUN DEC 16 2018 - 12Z THU DEC 20 2018  
   
..SIGNIFICANT PRECIPITATION FOR THE NORTHWEST
 
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
MODELS AND ENSEMBLES CONTINUE TO DIFFER ON THE TIMING/TRACK OF THE  
EMBEDDED SYSTEMS ACROSS THE LOWER 48, BUT FORECAST CLUSTERING HAS  
IMPROVED OVER THE PAST FEW RUNS. ACCORDINGLY, THE WPC MEDIUM RANGE  
PRODUCT SUITE WAS PRIMARILY DERIVED FROM A COMPOSITE BLEND OF  
MODELS AND ENSEMBLES, THE NATIONAL BLEND OF MODELS, AND WPC  
CONTINUITY, WITH MORE WEIGHTING APPLIED TO ENSEMBLE MEANS OVER  
TIME CONSISTENT WITH GRADUALLY GROWING FORECAST SPREAD.  
 
   
..PATTERN OVERVIEW AND WEATHER HIGHLIGHTS/HAZARDS
 
 
A LEAD MAIN SOUTHEAST/MID-ATLANTIC SYSTEM WILL SHIFT OFFSHORE  
SUNDAY. LINGERING WRAPBACK RAINS WILL SPREAD FROM THE MID-ATLANTIC  
TO SOUTHERN NEW ENGLAND BY EARLY NEXT WEEK AS THE COASTAL  
STORM/MARITIME THREAT LIFTS TO THE CANADIAN MARITIMES. ALSO EXPECT  
MODEST WINTRY WEATHER BACK OVER NORTHERN NEW ENGLAND WITH INFUSION  
OF UNCERTAIN NORTHERN STREAM ENERGY.  
 
A HEAVY PRECIPITATION AND HIGH WIND THREAT FOR THE PACIFIC  
NORTHWEST/NORTHERN CA RESURGES NEXT WEEK AS A SUCCESSION OF  
ENERGETIC PACIFIC SYSTEMS APPROACH THE REGION. SOME DEEPER LOWER  
LATITUDE MOISTURE TAP AND FLOW SUGGESTS FAVORED/HIGHER TERRAIN  
WILL FOCUS HEAVY RAINFALL/ELEVATION SNOWS, WITH SNOW WORKING TO  
THE NORTHERN GREAT BASIN/ROCKIES WITHIN A PRONOUNCED NORTHERN  
STREAM FLOW. MEANWHILE, A SPLIT/SEPARATED SOUTHERN STREAM TROUGH  
WILL CARVE OUT OVER THE SOUTHWEST U.S./NORTHERN MEXICO BY EARLY  
NEXT WEEK. UNCERTAIN SOUTHERN STREAM SYSTEM ENERGIES WILL THEN  
EJECT OUT ACROSS THE U.S. SOUTHERN TIER AND COULD INCREASINGLY TAP  
GULF OF MEXICO MOISTURE MID-LATER NEXT WEEK TO ENHANCE RAINFALL  
POTENTIAL.  
 
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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