667  
FXUS02 KWBC 071559  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1058 AM EST WED NOV 07 2018  
 
VALID 12Z SAT NOV 10 2018 - 12Z WED NOV 14 2018  
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
OVERALL, MODELS ARE IN GOOD AGREEMENT WITH THE SYNOPTIC SCALE  
FEATURES AND START DEVIATING SLIGHTLY BY LATER IN THE MEDIUM RANGE  
PERIOD. DURING THE WEEKEND, THE UPPER LOW OVER THE GREAT LAKES  
WILL SHIFT NORTH OVER CANADA AS ANOTHER TROUGH DEVELOPS ACROSS THE  
CENTRAL U.S. TO THE CENTRAL GREAT BASIN. THE UPPER LEVEL RIDGE  
WILL STAY OVER THE PACIFIC, JUST OFF THE WEST COAST. BY MONDAY AND  
INTO TUESDAY, AS THE UPPER LEVEL RIDGE BEGINS TO SHIFT INLAND, THE  
TROUGH WILL DIG ACROSS THE CENTRAL U.S. BY MIDWEEK, THE TROUGH  
WILL SHIFT OVER THE EASTERN U.S. AS THE UPPER LEVEL RIDGE CENTERS  
ITSELF OVER THE WESTERN U.S. HEIGHT FALLS ARE EXPECTED BY  
WEDNESDAY FOR THE PACIFIC NORTHWEST AS ENERGY FROM A TROUGH IN THE  
GULF OF ALASKA WORKS ITS WAY INTO THE REGION. THE OPERATIONAL 00Z  
AND 06Z GFS ALONG WITH THE 00Z ECMWF/UKMET WERE IN AGREEMENT WITH  
THE PATTERN ON DAYS 3/4 AND EVEN ON DAY 5. BY DAY 6, NOTICEABLE  
DIFFERENCES WITH TIMING OF THE TROUGH MOVING OVER THE EASTERN U.S.  
BECAME APPARENT. THE 00Z GFS WAS SIGNIFICANTLY FASTER BY DAY 7,  
HAVING A CLOSED UPPER LOW OVER EASTERN CANADA AS THE 06Z GFS/00Z  
ECMWF WERE STILL OVER THE OHIO/TENNESSEE VALLEY. THE 06Z GFS WAS  
ALSO SLIGHTLY FASTER--BUT STILL WITHIN A REASONABLE RANGE OF THE  
ECMWF. THE 00Z ECMWF ENSEMBLE MEAN AND 06Z GEFS MEAN SUGGEST TO  
LEAN TOWARD THE SLOWER SOLUTIONS. THUS, WPC USED A BLEND OF THE  
06Z GFS/00Z ECMWF/00Z UKMET IN THE BEGINNING OF THE MEDIUM RANGE,  
THEN SHIFTING TO MORE OF THE 00Z ECMWF ENSEMBLE MEAN/06Z GEFS MEAN  
BY DAYS 6 AND 7, WITH A LITTLE BIT OF THE 06Z GFS/00Z ECMWF.  
   
..WEATHER HIGHLIGHTS/THREATS
 
 
AS THE FIRST MID-UPPER LEVEL LOW LIFTS NORTHWARD FROM NEW ENGLAND,  
CYCLONIC FLOW OVER THE GREAT LAKES WILL ENCOURAGE LAKE EFFECT  
PRECIPITATION, SOME OF WHICH COULD BE SNOW, THAT MAY MOVE INTO THE  
INTERIOR OF NEW ENGLAND. AS THE SECOND TROUGH DIGS OVER THE  
CENTRAL U.S., MOISTURE WILL BE PULLED FROM THE GULF OF MEXICO AND  
INCREASE THE CHANCE OF SHOWERS AND THUNDERSTORMS ACROSS THE GULF  
COAST BY THE END OF THE WEEKEND AND INTO EARLY NEXT WEEK. AS THE  
TROUGH SHIFTS EAST, SO TOO WILL THE PRECIPITATION--SPREADING  
ACROSS THE TENNESSEE AND OHIO VALLEYS ALONG WITH THE MID-ATLANTIC  
ON TUESDAY AND INTO WEDNESDAY. IN FACT, THERE CONTINUES TO BE A  
GROWING SIGNAL SUPPORTING AMPLE LEADING WAVE/FRONTAL GENESIS AND  
DEEP MOISTURE RETURN TO WOULD FUEL HEAVY RAIN/CONVECTION EXPANSION  
NORTHWARD ACROSS THE EAST-CENTRAL THEN EASTERN U.S. ADDITIONALLY,  
MOISTURE FEEDING BACK INTO A SHARPENING BAROCLINIC ZONE COULD GIVE  
WAY TO ORGANIZED SNOW THREAT THROUGH THE APPALACHIANS/OHIO VALLEY,  
WITH AMPLE LAKE EFFECT ENHANCEMENT LEE OF THE GREAT LAKES AND FOR  
THE INTERIOR NORTHERN MID-ATLANTIC AND NORTHEAST WITH SYSTEM  
APPROACH. SIGNIFICANT EARLY SEASON SNOWS ARE POSSIBLE.  
 
AS THE PACIFIC TROUGH ENERGY MOVES INTO THE PACIFIC NORTHWEST, AN  
INCREASE IN PRECIPITATION CAN ALSO BE EXPECTED DURING THE MIDDLE  
OF NEXT WEEK. IN TERMS OF TEMPERATURES, THE EASTERN U.S. WILL BE  
ANOMALOUSLY COLD--FROM THE NORTHEAST SOUTHWARD TO THE GULF COAST.  
IN FACT, HIGH TEMPERATURES MAY ONLY REACH THE MID-50S ALONG THE  
WESTERN AND CENTRAL GULF COAST ON TUESDAY AND WEDNESDAY. THE UPPER  
AND MIDDLE MISSISSIPPI VALLEY MAY SEE HIGH TEMPERATURES ONLY REACH  
THE MID 20S TO MID 30S. THE WESTERN U.S. WILL CONTINUE TO  
EXPERIENCE ABOVE AVERAGE TEMPERATURES.  
 
REINHART/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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