167  
FXUS02 KWBC 121548  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1048 AM EST WED DEC 12 2018  
 
VALID 12Z SAT DEC 15 2018 - 12Z WED DEC 19 2018  
   
..SIGNIFICANT PRECIPITATION FOR THE NORTHWEST
 
 
   
..OVERVIEW AND GUIDANCE EVALUATION/PREFERENCES
 
 
A DEEP CLOSED LOW WILL EXIT OFF THE SOUTHERN MID-ATLANTIC COAST  
LATE THIS WEEKEND AND TAKE ITS FRONTAL SYSTEM INTO THE ATLANTIC,  
PAVING THE WAY FOR A DRY PERIOD IN THE EAST EARLY NEXT WEEK. THE  
PACIFIC NORTHWEST WILL REMAIN QUITE ACTIVE AS SEVERAL SYSTEMS PUSH  
INTO/THROUGH THE REGION DOWNSTREAM OF A STRONG 170KT+ CENTRAL  
PACIFIC JET. THE MODELS AND ENSEMBLES CONTINUE TO DIFFER ON THE  
TIMING/TRACK OF THE EMBEDDED SYSTEMS ACROSS THE LOWER 48, BUT THE  
ECMWF ENSEMBLE MEAN AGAIN SEEMED TO BE THE BEST BASE OF THE  
FORECAST, FOLLOWED BY THE 00Z ECMWF AS THEY HAVE BEEN SLOWER WITH  
THE EXITING CLOSED LOW OUT OF THE SOUTHEAST THAN THE GFS/GEFS  
(WHICH HAVE TRENDED SLOWER). THIS STAYED CLOSE TO WPC CONTINUITY  
WITH THE PROGRESSION OF SYSTEMS.  
 
   
..WEATHER HIGHLIGHTS AND HAZARDS
 
 
SOUTHEASTERN/MID-ATLANTIC FRONTAL SYSTEM WILL EXIT THE COAST ALONG  
WITH SOME LOCALLY HEAVIER RAIN (MOSTLY IN THE SHORT RANGE PERIOD)  
AND PERHAPS SOME WINTRY WEATHER IN NORTHERN NEW ENGLAND.  
TEMPERATURES WILL GENERALLY BE NEAR TO ABOVE AVERAGE EXCEPT OVER  
FLORIDA BEHIND THE FRONT THIS WEEKEND AND THE NORTHEAST EARLY NEXT  
WEEK AS A NORTHERN STREAM COLD FRONT PASSES THROUGH.  
 
UPSTREAM, PRECIPITATION/WIND SUBSTANTIALLY INCREASES FROM COASTAL  
WASHINGTON TO NORTHERN CA THROUGH THE WEEKEND WITH RESURGENCE  
EARLY-MID NEXT WEEK AS A SUCCESSION OF 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. WHILE THIS ACTIVITY REMAINS CONCENTRATED WITHIN A  
PRONOUNCED NORTHERN STREAM FLOW, A SEPARATED SOUTHERN STREAM  
TROUGH WILL CARVE OUT OVER THE SOUTHWEST U.S./NORTHERN MEXICO  
AROUND TUESDAY. THIS ASSOCIATED SURFACE SYSTEM MAY TAP WESTERN  
GULF MOISTURE MIDWEEK NEXT WEEK WITH AN INCREASE IN RAINFALL ALONG  
THE RIO GRANDE.  
 
FRACASSO/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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