037  
FXUS02 KWBC 241600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1100 AM EST SAT NOV 24 2018  
 
VALID 12Z TUE NOV 27 2018 - 12Z SAT DEC 01 2018  
   
..PATTERN OVERVIEW
 
 
THE MEDIUM RANGE PERIOD BEGINS TUESDAY WITH A LARGE SCALE UPPER  
LEVEL CLOSED TROUGH CENTERED OVER THE GREAT LAKES REGION WITH  
MULTIPLE EMBEDDED SHORTWAVES PIVOTING AROUND IT, AND BROAD  
TROUGHING OVER THE EASTERN PACIFIC WITH A DOWNSTREAM RIDGE AXIS  
OVER THE INTERMOUNTAIN WEST. THE LARGE CLOSED LOW SLOWLY EXITS THE  
NORTHEAST U.S. ON THURSDAY WITH QUASI-ZONAL FLOW LIKELY BECOMING  
ESTABLISHED OVER MUCH OF THE CENTRAL U.S. AND A LARGE SCALE TROUGH  
IS EXPECTED TO MOVE INLAND ACROSS THE WESTERN U.S. AS THE  
MID-UPPER LEVEL TROUGH EXITS THE ROCKIES IN AN EMERGING/ENERGETIC  
SOUTHERN STREAM, THE FLOW WILL BECOME INCREASINGLY FAVORABLE FOR  
PLAINS/MS VALLEY SYSTEM GENESIS TO OPEN DECEMBER. THIS WOULD BE  
COINCIDENT WITH THE BUILDING OF DOWNSTREAM RIDGE OVER THE EASTERN  
U.S.  
 
   
..MODEL GUIDANCE AND UNCERTAINTY ASSESSMENT
 
 
THE WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY DERIVED FROM A  
COMPOSITE BLEND OF THE NOW QUITE REASONABLY WELL CLUSTERED  
GUIDANCE OVER THE LOWER 48 FROM THE 00 UTC GEFS/NAEFS/ECMWF  
ENSEMBLE MEANS AND LATEST GFS/ECMWF DETERMINITIC MODELS THROUGH  
THU.  
INCREASING FORECAST SPREAD AND RUN TO RUN INCONSISTENCIES,  
ESPECIALLY OVER THE EASTERN PACIFIC THEN SUGGESTED USAGE OF ONLY  
THESE STILL REASONABLY COMPATABLE ENSEMBLE MEANS INTO NEXT FRI/SAT  
(DAYS 6/7).  
 
   
.WEATHER HIGHLIGHTS/THREATS
 
 
INLAND WRAPPING HEAVY SNOW SHOULD EXIT NORTHERN NEW ENGLAND  
WEDNESDAY, BUT LOW LEVEL COLD AIR ADVECTION/HIGH WINDS IN THE WAKE  
OF THE SYSTEM WILL SUPPORT LINGERING LAKE EFFECT SNOWS INTO  
THURSDAY. OUT WEST, THE HEAVIEST PRECIPITATION SHOULD FOCUS FROM  
THE PACIFIC NORTHWEST TO CENTRAL CA AS TWO MAIN ENERGETIC PACIFIC  
STORM SYSTEMS MOVE ONSHORE AND BRING ENHANCED MOISTURE INTO THESE  
AREAS, WITH AN ATMOSPHERIC RIVER EVENT POSSIBLE BY TUESDAY INTO  
NORTHERN CALIFORNIA. IN ADDITION TO THE HEAVY RAINFALL AND LOCAL  
RUNOFF THREAT, HEAVY SNOW IS LIKELY FOR THE HIGHER MOUNTAINS FROM  
THE CASCADES AND SIERRA TO THE CENTRAL AND NORTHERN ROCKIES.  
SUBSEQUENT SYSTEM PROGRESSION/GENESIS OVER THE CENTRAL U.S. INTO  
NEXT WEEKEND MAY LEAD TO PRONOUNCED LEAD GULF MOISTURE INFLOW TO  
FUEL AN EXPANDING AREA OF PRECIPITATION.  
 
TEMPERATURES ARE EXPECTED TO BE ON THE ORDER OF 15 TO 20 DEGREES  
BELOW AVERAGE FROM THE NORTHERN PLAINS TO THE OHIO VALLEY ON  
TUESDAY AND WEDNESDAY BEFORE A MODERATION TREND ENSUES BY LATER IN  
THE WEEK. AREAS WITH FRESH SNOW COVER ACROSS THE MIDWEST IN THE  
WAKE OF THE WINTER STORM MAY HAVE OVERNIGHT LOWS DROPPING WELL  
INTO THE SINGLE DIGITS FOR THE EARLY TO MIDDLE PART OF THE  
UPCOMING WORK WEEK, WITH SOME READINGS POSSIBLY FALLING BELOW ZERO  
WHERE WINDS ARE LIGHT AND SKIES CLEAR OUT. TEMPERATURES SHOULD  
GENERALLY BE WITHIN 5-10 DEGREES OF CLIMATOLOGICAL AVERAGES FOR  
THE WESTERN THIRD OF THE NATION.  
 
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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