646  
FXUS02 KWBC 081558  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1058 AM EST SAT DEC 08 2018  
 
VALID 12Z TUE DEC 11 2018 - 12Z SAT DEC 15 2018  
   
..HEAVY RAIN THREAT FOR THE EAST LATE NEXT WEEK
 
 
   
..OVERVIEW AND GUIDANCE EVALUATION/PREFERENCES
 
 
THE WEATHER PATTERN IS EXPECTED TO REMAIN QUITE ACTIVE IN THE  
PACIFIC NORTHWEST AND BECOME INCREASINGLY WET IN MUCH OF THE EAST  
LATER IN THE WEEK NEXT 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. GENERALLY  
FAVORED THE DETERMINISTIC MODELS NEAREST THE ENSEMBLE MEAN  
CONSENSUS AND CONTINUITY WHICH INCLUDED THE 00Z GFS/ECMWF. BY NEXT  
FRI/SAT, WITH UPPER RIDGING OVER HUDSON BAY AND DEEP TROUGHING IN  
THE BERING SEA, TELECONNECTIONS FAVOR A CLOSED LOW THROUGH THE  
TENNESSEE AND OHIO VALLEYS WITH A SURFACE LOW TRACK ON THE WEST  
SIDE OF THE APPALACHIANS TOWARD THE EASTERN GREAT LAKES. WITH A  
TREND TOWARD INCREASED AMPLITUDE, FAVORED THE SLOWER HALF OF THE  
SOLUTIONS (I.E., 00Z GFS/ECMWF) AS THE ENSEMBLE TREND HAS BEEN  
SLOWER OVERALL THE PAST SEVERAL CYCLES. IN THE WEST, A BLENDED  
SOLUTION SHOULD SUFFICE DOWNWIND OF A STRONG PACIFIC JET.  
 
   
..WEATHER HIGHLIGHTS AND HAZARDS
 
 
A DEPARTING COASTAL LOW OFF THE CAROLINAS TUESDAY OFFERS A  
LINGERING MARITIME GALE HAZARD BEING FOLLOWED BY OPC. IN THE WAKE  
OF THE LOW, COOL TEMPERATURES AND REINFORCING DRY HIGH PRESSURE  
WILL KEEP TEMPERATURES BELOW AVERAGE EAST OF THE MISSISSIPPI  
THROUGH MIDWEEK. ABOVE AVERAGE TEMPERATURES WILL OUTRUN THE LEAD  
AND SECONDARY PACIFIC SYSTEMS THROUGH THE PLAINS TUE-THU BEFORE  
SURGING INTO THE EAST FRI/SAT.  
 
OUT WEST, PRECIPITATION AND WIND WILL PERIODICALLY INCREASE  
EARLY-MID NEXT WEEK AND INTO NEXT WEEKEND AS HEIGHTS FALL WITH A  
SUCCESSION OF APPROACHING SHORTWAVES/FRONTAL SYSTEMS. HIGHER  
TERRAIN OF WESTERN OREGON/WASHINGTON HAVE THE POTENTIAL FOR  
HEAVIEST PRECIPITATION AMOUNTS (RAIN AND MOUNTAIN SNOW) AS THE  
SYSTEMS MOVE INLAND INTO THE NORTH-CENTRAL GREAT BASIN/ROCKIES.  
 
BY LATE WEDNESDAY INTO THURSDAY, SECONDARY PACIFIC SHORTWAVE WILL  
DIVE THROUGH THE ROCKIES INTO THE SOUTHERN PLAINS AND  
OVERTAKE/REINFORCE UPPER TROUGHING WHILE SPAWNING CYCLOGENESIS AT  
THE SURFACE OVER OKLAHOMA. GULF MOISTURE WILL INCREASE AHEAD OF  
THE SYSTEM HELPING TO EXPAND THE PRECIPITATION SHIELD TO THE EAST  
AND THEN WRAPPED AROUND TO THE NORTH OF THE SURFACE LOW.  
RELATIVELY SLOW MOVEMENT OF THE SYSTEM WILL SUPPORT A HEAVY RAIN  
THREAT AND SOME COLD SECTOR SNOW THROUGH THE MIDWEST/GREAT LAKES  
REGION TO THE NORTHWEST OF THE LOW TRACK. RAINFALL MAY BE HEAVY  
ALONG THE EAST SIDE OF THE APPALACHIANS TO THE COASTAL PLAIN WITH  
THE INFUSION OF ATLANTIC MOISTURE AS WELL, WHICH COULD FALL OVER  
AREAS THAT RECEIVE APPRECIABLE SNOWFALL OVER THE NEXT COUPLE OF  
DAYS (SOUTHERN APPALACHIANS).  
 
FRACASSO  
 
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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