906  
FXUS02 KWBC 071601  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1200 PM EDT FRI SEP 07 2018  
 
VALID 12Z MON SEP 10 2018 - 12Z FRI SEP 14 2018  
   
..HEAVY RAINFALL TO EXIT THE NORTHEAST EARLY NEXT WEEK
 
 
   
..HURRICANE FLORENCE LOOMS OFF THE EAST COAST LATER IN THE WEEK
 
 
   
..PATTERN OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
AT THE START OF THE PERIOD, THE EXTRATROPICAL REMAINS OF GORDON  
WILL BE IN THE PROCESS OF PUSHING EASTWARD ACROSS LAKE ERIE. BROAD  
MID-LEVEL SOUTHWESTERLY FLOW SHOULD USHER THE SYSTEM TOWARD  
SOUTHERN QUEBEC BY THE FOLLOWING DAY. AS THIS EXITS THE MAP  
DOMAIN, THE FOCUS SHIFTS TOWARD THE EASTERN PACIFIC AND WEST COAST  
AS A POSITIVELY-TILTED LONGWAVE TROUGH SITS OVER THE REGION DURING  
DAY 5-7, SEPTEMBER 12-14. THIS CONFIGURATION WILL AFFORD  
SIGNIFICANT HEIGHT RISES ACROSS THE CENTRAL/EASTERN U.S. WITH  
ANOMALIES AROUND 2 TO 2.5 SIGMA UNDER THE CORE OF THE UPPER RIDGE.  
TO ITS SOUTH, MODELS ARE HINTING AT SOME BROAD WEAKNESS ACROSS THE  
WESTERN GULF COAST. LASTLY, INFLUENCES OF HURRICANE FLORENCE MAY  
REACH THE EASTERN SEABOARD DURING THE MIDDLE TO LATTER PART OF  
NEXT WEEK. WHILE OCEANIC IMPACTS WILL BE THE PRIMARY ISSUE,  
EVENTUAL COASTAL TO INLAND EFFECTS ARE POSSIBLE DEPENDING ON THE  
ULTIMATE TRACK.  
 
MULTI-DAY ENSEMBLE SPAGHETTI PLOT COMPARISONS HAVE SHOWN ONLY  
MODEST CHANGES IN THE GUIDANCE WITH RESPECT TO THE AMPLIFIED  
SYNOPTIC-SCALE FLOW. WHILE INDIVIDUAL MEMBERS EXHIBIT SOME  
VARIATIONS IN THE PATTERN, OPERATIONAL AND ENSEMBLE GUIDANCE  
AFFORD A FAIRLY CONFIDENT FORECAST, PARTICULARLY ACROSS THE  
WESTERN U.S. A GENERAL CONSENSUS OF SOLUTIONS IS WARRANTED  
ALTHOUGH THE 00Z UKMET DID SEEM TO BE A HAIR QUICK EJECTING THE  
MEAN TROUGH DOWNSTREAM. ON THE OTHER HAND, THE FORECAST TRACK OF  
HURRICANE FLORENCE REMAINS HIGHLY VOLATILE BEYOND DAY 5/WEDNESDAY.  
POTENTIAL LANDFALL COULD BE ANYWHERE FROM THE EASTERN FLORIDA  
PANHANDLE UP TO THE MID-ATLANTIC LATE NEXT WEEK WHILE OTHER  
SCENARIOS TURN THE CIRCULATION NORTH AND EAST BEFORE REACHING THE  
COAST. WHILE FOCUS IS ON THE INDIVIDUAL CYCLONE TRACK, IMPACTS FAR  
AWAY FROM THE CENTER ARE LIKELY GIVEN THE EXPECTED INCREASE IN THE  
STRENGTH THE NEXT FEW DAYS. PLEASE VISIT THE NATIONAL HURRICANE  
CENTER WEBSITE FOR MORE INFORMATION ON FLORENCE.  
 
A GENERAL BLEND OF OPERATIONAL SOLUTIONS WAS UTILIZED FOR THE  
FIRST COUPLE OF DAYS OF THE PERIOD. THIS WAS COMPRISED OF THE 06Z  
GFS AND 00Z GFS-PARALLEL/ECMWF RUNS WHILE SLOWING ADDING ENSEMBLE  
MEANS INTO THE PICTURE THEREAFTER. DID KEEP A MODEST AMOUNT OF THE  
06Z GFS/00Z GFS-PARALLEL IN THE MIX THROUGHOUT GIVEN IT WAS THE  
CLOSEST MATCH TO THE OFFICIAL TRACK OF HURRICANE FLORENCE.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
INITIALLY, HEAVY RAINFALL WILL REMAIN AN ISSUE AS GORDON AND THE  
ATTENDANT FRONTAL BOUNDARY INTERCEPT ABUNDANT TROPICAL MOISTURE.  
THIS SHOULD PRIMARILY FOCUS OVER NEW ENGLAND BEFORE WINDING DOWN  
LATER ON TUESDAY AS MID-LEVEL HEIGHTS BEGIN TO RISE. OVER THE  
PACIFIC NORTHWEST, PERSISTENT ONSHORE WITHIN THE MEAN TROUGH WILL  
KEEP PRECIPITATION IN THE FORECAST DURING MUCH OF THE PERIOD.  
FARTHER EAST, A COUPLE WAVES OF LOW PRESSURE SHOULD SPREAD A  
SHIELD OF RAINFALL ACROSS THE NORTH-CENTRAL U.S. BEFORE LIFTING  
INTO CENTRAL CANADA. ELSEWHERE, SOME LINGERING HEAVY RAINFALL  
THREAT IS POSSIBLE NEAR THE UPPER LOW ACROSS THE WESTERN GULF OF  
MEXICO. THIS WOULD FOCUS OVER THE WESTERN/CENTRAL GULF COAST  
ALTHOUGH SOME SPREAD EXISTS IN THE GUIDANCE. AND ALONG THE EASTERN  
SEABOARD, THE PRIMARY IMPACTS WILL BE DRIVEN BY THE TRACK OF  
HURRICANE FLORENCE. FLOODING RAINS, HIGH WINDS, ROUGH SURF, AMONG  
OTHERS WOULD ALL BE POSSIBLE BUT IT IS TOO EARLY TO PINPOINT EXACT  
IMPACTS GIVEN THE MODEL UNCERTAINTIES.  
 
REGARDING THE TEMPERATURE FORECAST, COOL WEATHER SHOULD PREVAIL  
FROM NORTHERN CALIFORNIA UP INTO THE PACIFIC NORTHWEST GIVEN THE  
TROUGH OVERHEAD. FORECAST ANOMALIES SHOULD SIT AROUND 5 TO 10  
DEGREES BELOW CLIMATOLOGY DURING MUCH OF THE WEEK. DOWNSTREAM INTO  
THE MIDDLE OF THE COUNTRY, BUILDING HEIGHTS WILL SUPPORT ABUNDANT  
WARMTH FOR SEVERAL DAYS. FARTHER EAST, THE TEMPERATURE FORECAST  
WILL BE HIGHLY DEPENDENT ON THE TRACK OF FLORENCE BUT WARM  
CONDITIONS ARE LIKELY INITIALLY GIVEN THE UPPER RIDGE IN PLACE.  
 
RUBIN-OSTER  
 
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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