965  
FXUS02 KWBC 031600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1200 PM EDT MON SEP 03 2018  
 
VALID 12Z THU SEP 06 2018 - 12Z MON SEP 10 2018  
   
..PATTERN OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
GUIDANCE CONTINUES TO ADVERTISE RELATIVELY PROGRESSIVE MEAN FLOW  
ACROSS THE NORTHERN CONTIGUOUS U.S. AND SOUTHERN CANADA INTO THE  
WEEKEND, WITH A TENDANCY TO AMPLIFY INTO NEXT WEEK DOWNSTREAM FROM  
A NORTHEAST PACIFIC TROUGH THAT EXISTS IN RESPONSE TO A VERY  
STRONG BERING SEA RIDGE. WITHIN THIS RIDGE, GUIDANCE SUGGESTS  
POTENTIAL FOR HEIGHTS THAT COULD REACH 3-4 STANDARD DEVIATIONS  
ABOVE CLIMATOLOGY LATE IN THE WEEK. THIS SEEMS REASONABLE AS THE  
RIDGE ITSELF IS DOWNSTREAM OF A EXTRATROPICAL LOW ASSOCIATED WITH  
CURRENT WESTERN PACIFIC TYPHOON JEBI THAT IS FORECAST TO LIFT INTO  
THE HIGH LATITUDES. MEANWHILE, FLOW AROUND A WEAKENING EASTERN  
U.S. RIDGE ALOFT SHOULD GUIDE CURRENT TROPICAL STORM GORDON INTO  
SOUTH-CENTRAL U.S. MID-LATER WEEK. FARTHER EAST, THIS MAY ALLOW AN  
INVERTED UPPER TROUGH/RAINFALL FOCUS TO WORK FROM THE BAHAMAS INTO  
FLORIDA.  
 
THE WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY DERIVED FROM THE  
00 UTC ECMWF THU-SAT WHOSE INLAND TRACK OF WEAKENING BUT STILL  
HEAVY RAIN PRODUCING GORDON SEEMS THE CLOSEST GUIDANCE MATCH TO  
THE LATEST NHC FORECAST TRACK. HOWEVER, THIS ECMWF RUN IS  
SEEMINGLY TOO PROGRESSIVE WITH NORTHEASTERN PACIFIC TO PACIFIC  
NORTHWEST STORM ENERGIES/HEIGHT FALLS INTO DAYS 6/7 GIVEN UPSTREAM  
FLOW AMPLITUDE. ACCORDINGLY, QUICKLY TRANSITIONED GUIDANCE  
PREFERENCE MORE IN LINE WITH 06 UTC GEFS MEAN AND 00 UTC ECMWF  
ENSEMBLE MEAN TO ACCOUNT FOR THIS UPSTREAM FLOW ISSUE. THE  
SUBSEQUENT TRACK OF GORDON MEANWHILE MAY STILL BE IN LINE IN THIS  
ECMWF RUN.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
TROPICAL STORM GORDON HAS DEVELOPED NEAR SOUTHERN FL. BY LATER  
WEEK INTO MEDIUM RANGE TIME SCALES, THERE WILL BE A SUBSTANTIAL  
THREAT FOR LOCALLY HEAVY RAINFALL FOR PARTS OF THE SOUTH-CENTRAL  
PLAINS/MID-LOWER MS VALLEY AND VICINITY NEAR THE PATH OF SLOWLY  
WEAKENING GORDON AS PER NHC AND NORTHEASTWARD AS AN EXTRATROPICAL  
LOW OVER THE MIDWEST/GREAT LAKES INTO DAYS 6/7 AS PER WPC. DEEP  
TROPICAL MOISTURE WILL FEED INTO A LARGER SCALE BAND OF MOISTURE  
EXTENDING FROM THE SOUTHERN PLAINS NORTHEASTWARD, INTERACTING WITH  
THE FRONT THAT STALLS OVER MID-LATITUDES OF THE LOWER 48 AND THEN  
LIFTS NORTHEASTWARD AS A WARM FRONT. SIGNIFICANT DETAILS HAVE YET  
TO BE RESOLVED SO CONFIDENCE IS NOT YET AS HIGH AS DESIRED FOR  
PINPOINTING THE BEST FOCUS FOR HIGHEST RAINFALL AMOUNTS WITHIN A  
FAVORED ZONE FROM THE SOUTHERN-CENTRAL PLAINS THROUGH THE MIDWEST  
INTO PARTS OF THE NORTHERN MID-ATLANTIC/NORTHEAST. MID LEVEL  
ENERGY AND A SURFACE TROUGH REACHING FLORIDA FROM THE BAHAMAS MAY  
ENHANCE RAINFALL AT TIMES OVER/NEAR THAT STATE, WHILE LINGERING  
MOISTURE MAY AID SOME ACTIVITY ALONG PORTIONS OF THE GULF COAST.  
THE PACIFIC NORTHWEST SHOULD SEE A PERIOD OF LIGHT-MODERATE  
PRECIPITATION LATE WEEK INTO THE WEEKEND WITH POTENTIALLY ANOTHER  
AROUND THE START OF NEXT WEEK.  
 
EXPECT VERY WARM AND HUMID CONDITIONS OVER THE EAST LATE THIS WEEK  
AHEAD OF THE BACKDOOR FRONT THAT REACHES INTO THE MID-ATLANTIC.  
THE BEST SIGNAL FOR MOST EXTREME ANOMALIES (AT LEAST PLUS 10-15F)  
CONTINUES TO BE FOR MIN TEMPS FROM THE OHIO VALLEY/APPALACHIANS  
INTO MID-ATLANTIC/NORTHEAST WITH SOME READINGS POSSIBLY EXCEEDING  
DAILY RECORD WARM MIN VALUES. CLOUDS/RAINFALL WILL TEMPER HIGH  
TEMPERATURES OVER THE EAST AFTER FRI BUT KEEP THE LOWS FAIRLY  
WARM.  
 
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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