920  
FXUS02 KWBC 081558  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1058 AM EST THU NOV 8 2018  
 
VALID 12Z SUN NOV 11 2018 - 12Z THU NOV 15 2018  
 
***BELOW NORMAL TEMPERATURES FOR MUCH OF THE U.S. WITH SOME EARLY  
SEASON SNOW POSSIBLE FROM THE GREAT LAKES TO INTERIOR NEW  
ENGLAND***  
 
16Z UPDATE  
----------  
THE DETERMINISTIC MODELS AND THEIR RESPECTIVE MEANS ARE IN ABOVE  
AVERAGE AGREEMENT ON THE SYNOPTIC SCALE FOR THE BEGINNING OF THE  
FORECAST PERIOD OWING TO THE HIGH AMPLITUDE PATTERN IN PLACE, WITH  
AN UPPER RIDGE OFF THE WEST COAST, A TROUGH OVER THE NORTH-CENTRAL  
U.S., AND A BROAD SUBTROPICAL RIDGE OVER THE SOUTHERN GULF OF  
MEXICO. THE COMPLEXITY IN THE FORECAST RELATES TO THE AMOUNT OF  
EVENTUAL PHASING BETWEEN THE INITIAL NORTHERN STREAM AND SOUTHERN  
STREAM SHORTWAVE PERTURBATIONS WITHIN THE LARGE SCALE SYNOPTIC  
TROUGH AXIS, AND THESE DIFFERENCES BECOME APPARENT BY DAY 5 ON  
TUESDAY. THE OPERATIONAL GFS BECOMES FASTER WITH THE LARGE EAST  
COAST STORM SYSTEM COMPARED TO THE MODEL CONSENSUS, BUT GIVEN A  
FASTER TREND IN THE ECMWF OVER THE PAST 24 HOURS, THE GFS SCENARIO  
CERTAINLY SEEMS PLAUSIBLE. ELSEWHERE ACROSS THE CONTINENTAL U.S.,  
THE CMC BECOMES OUT OF PHASE WITH THE UPPER LEVEL PATTERN ACROSS  
THE NORTHWESTERN U.S. BY TUESDAY SINCE THE SHORTWAVE OVER THE  
NORTHEAST PACIFIC BECOMES MUCH MORE PROGRESSIVE THAN THE MODEL  
CONSENSUS. THE WPC FORECAST INCORPORATED MORE OF THE EC MEAN BY  
TUESDAY, AND THEN ALSO SOME OF THE GEFS MEAN BY THE END OF THE  
FORECAST PERIOD. THE PREVIOUS DISCUSSION FOLLOWS BELOW FOR  
REFERENCE.  
 
D. HAMRICK  
   
..GUIDANCE/UNCERTAINTY ASSESSMENT
 
 
GFS/ECMWF AND GEFS/ECMWF ENSEMBLE SOLUTIONS ARE WELL CLUSTERED  
INTO EARLY NEXT WEEK, BUT BECOME INCREASING VARIED WITH SMALLER  
SCALE SYSTEM DETAILS INTO NEXT MID-LATE WEEK WHEN A COMPOSITE  
BLEND OF ENSEMBLE MEANS IS PREFERRED. THIS SOLUTION MAINTAINS GOOD  
WPC CONTINUITY.  
   
..WEATHER HIGHLIGHTS/THREATS
 
 
A STORM TRACK TO THE NORTHEAST PACIFIC/GULF OF ALASKA MAINTAINS AN  
AMPLIFIED RIDGE AXIS ALOFT ALONG/OFFSHORE WESTERN NORTH AMERICA  
INTO EARLY NEXT WEEK. DOWNSTREAM CLIPPER LOW TRACK AND FAVORABLE  
DYNAMICS WILL SQUEEZE OUT A SWATH OF SNOW IN COOLED AIR OF THE  
GREAT LAKES/NORTHEAST. MEANWHILE, POTENT WEEKEND SHORTWAVE DIGGING  
THROUGH THE INTERMOUNTAIN WEST/ROCKIES WILL FAVOR A LEAD SNOW  
BURST OVER THE SOUTH-CENTRAL ROCKIES SUNDAY TO SPILL INTO THE  
PLAINS AS AIDED BY COLD POST-FRONTAL UPSLOPE FLOW.  
 
THE UPPER TROUGH WILL AMPLIFY OVER THE CENTRAL U.S. EARLY NEXT  
WEEK WITH INCREASING NORTHERN AND SOUTHERN STREAM PHASING TO THE  
LEE OF THE AMPLIFIED BUT GRADUALLY INLAND SHIFTING UPSTREAM RIDGE.  
LEAD WAVE/FRONTAL GENESIS AND DEEP MOISTURE RETURN WILL FUEL HEAVY  
RAIN/CONVECTION EXPANSION NORTHWARD ACROSS THE EAST-CENTRAL THEN  
EASTERN U.S. MOISTURE FEEDING BACK INTO A SHARPENING BAROCLINIC  
ZONE MEANWHILE PRESENTS AN ORGANIZED SNOW THREAT THROUGH THE  
APPALACHIANS/OHIO VALLEY, WITH AMPLE LAKE EFFECT ENHANCEMENT LEE  
OF THE GREAT LAKES. THERE IS CONTINUED UNCERTAINTY WITH RESPECT TO  
THE LEAD COASTAL/INLAND LOW TRACK AND WESTERN EXTENT OF THE MAIN  
PRECIPITATION SHIELD/COLD AIR WITH RECENT ECMWF RUNS OFFERING A  
MORE INLAND TRACK THAN MORE COASTAL TRACKS FROM RECENT GFS RUNS. A  
LARGER PERCENTAGE OF GEFS AND ECMWF ENSEMBLE MEMBERS FAVOR THE  
COASTAL SOLUTION BUT THE MINORITY SUBSET OF MORE INLAND SOLUTIONS  
CANNOT BE RULES OUT CONSIDERING THE AMPLITUDE AND WESTWARD  
POSITION OF THE MAIN MID-UPPER LEVEL TROUGH. ENSEMBLE MEANS OFFER  
A DECENT COMPROMISE AT THIS POINT. OVERALL, THERE IS A THREAT FOR  
HEAVY GREAT LAKES/OH VALLEY/APPALACHIANS TO INTERIOR NORTHEAST  
EARLY SEASON SNOWS.  
 
WELL UPSTREAM, PACIFIC TROUGH ENERGY AND HEIGHT FALLS START TO  
WORK INTO THE NORTHWEST EARLY-MID NEXT WEEK AS THE LEAD/AMPLIFIED  
RIDGE ALOFT GRADUALLY/FINALLY SHIFTS INLAND. THIS SUPPORTS AN  
INCREASED CHANCE FOR PRECIPITATION INCLUDING MODEST ELEVATION  
SNOWS.  
 
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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