010  
FXUS02 KWBC 070543  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
143 AM 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
 
 
UPPER PATTERN OVER THE LOWER 48 WILL FEATURE A RELOADING TROUGH IN  
THE WEST WITH RIDGING IN THE WESTERN ATLANTIC NEXT WEEK. THIS WILL  
CARRY THE REMNANTS OF GORDON NORTHEASTWARD THROUGH THE ST.  
LAWRENCE VALLEY ALONG A FRONT BUT MAY OPEN THE DOOR FOR FLORENCE  
TO TRACK VERY NEAR THE EAST COAST LATER IN THE WEEK. UNCERTAINTY  
IS HIGH IN ITS TRACK AS THE ENSEMBLE SPREAD SPANS FROM FLORIDA TO  
NOVA SCOTIA BY NEXT THURSDAY. UPSTREAM PATTERN REMAINS QUITE  
AMPLIFIED OVER THE PACIFIC (VERY STRONG UPPER HIGH IN THE BERING  
SEA AND A DEEP UPPER LOW NEAR 40N/180 EARLY IN THE WEEK) AND  
TELECONNECTONS FAVOR A POSITIVELY TILTED TROUGH IN THE WEST AND  
RIDGING IN THE WESTERN ATLANTIC WHICH IS JUST WHAT THE ENSEMBLES  
CONTINUE TO FORECAST.  
 
A BLEND OF THE RECENT DETERMINISTIC GUIDANCE SUFFICED TO START AS  
THE SFC LOW ASSOCIATED WITH GORDON ACCELERATES NORTHEASTWARD. THE  
ATTENDANT COLD FRONT WILL STALL ACROSS THE MID-ATLANTIC AS  
FLORENCE LIKELY MOVES WEST OF 70W ON WEDNESDAY. FRONT IN THE WEST  
WILL SOUTHWARD AND EASTWARD AS THE TROUGH RELOADS, WITH LESS  
AGREEMENT ON THE TRAILING SHORTWAVE LATER IN THE WEEK. THAT WILL  
STALL OVER THE DAKOTAS AND BACK TO THE CENTRAL ROCKIES/GREAT BASIN  
AS IT ALIGNS WITH THE UPPER SW FLOW.  
 
FOR NEXT THU/FRI IN THE EAST, EVOLUTION OF THE UPPER HIGH AROUND  
FLORENCE WILL DICTATE ITS WESTWARD EXTENT. FOR NOW, CONTINUED WITH  
A CURVE TO THE N JUST OFFSHORE THE DELMARVA AND NJ PER THE CENTRAL  
CLUSTER MEAN (AMONG THE ENSEMBLE SYSTEMS), ROUGHLY BETWEEN THE 12Z  
GFS AND ECMWF. THIS ALIGNED WELL WITH YESTERDAY'S WPC/NHC  
COORDINATION CALL. WILL NEED A COUPLE MORE DAYS TO DECREASE THE  
UNCERTAINTY FROM "ANYTHING IS POSSIBLE" (~1500 MILES OF SPREAD) TO  
SOMETHING MORE REASONABLE.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
HEAVY RAIN ASSOCIATED WITH EX-GORDON WILL ONLY SLOWLY ABATE AS  
PRECIPITABLE WATER VALUES AND ANOMALIES (1.5-2" AND +2 SIGMA)  
SURGE AHEAD OF THE FRONT. HURRICANE FLORENCE WILL LIKELY PROVIDE  
THE GREATEST UNCERTAINTY FOR SENSIBLE WEATHER EFFECTS NEAR THE  
EAST COAST. EVEN IF THE TRACK REMAINS FAR ENOUGH OFFSHORE TO KEEP  
THE REGION MOSTLY DRY, SOME COASTAL AREAS MAY SEE BRISK WINDS WITH  
LOTS OF WAVES OFFSHORE -- SEE OPC FOR MORE INFORMATION ON THE  
WIND/WAVE POTENTIAL. OTHER AREA OF RAINFALL LATER IN THE WEEK MAY  
BE ALONG THE UPPER GULF COAST WITH A WEAKNESS ALOFT IN THE REGION  
ATOP PLENTY OF MOISTURE.  
 
THE EVOLVING PATTERN OVER THE EASTERN PACIFIC/WESTERN NORTH  
AMERICA WILL BRING MOISTURE INTO THE PACIFIC NORTHWEST WITH  
PRECIPITATION LIKELY PERSISTING THROUGH THE END OF THE PERIOD.  
UPPER TROUGH WILL BRING MULTIPLE DAYS OF HIGHS 5-10F BELOW AVERAGE  
NEXT WEEK TO WASHINGTON/OREGON BUT ABOUT 5-15F ABOVE AVERAGE FROM  
THE SOUTHWEST INTO THE NORTHERN PLAINS. IN THE EAST, NEAR AVERAGE  
HIGH TEMPERATURES WILL PERSIST ALONG THE DISSIPATING FRONT BUT  
WILL BE DEPENDENT ON THE TRACK OF FLORENCE AS MOST OF THE RAIN  
COULD STAY OFFSHORE WITH THE I-81/95 CORRIDORS IN AN AREA OF  
SUBSIDENCE OUTSIDE THE CIRCULATION. FOR NOW, MAINTAINED A CHANCE  
OF RAIN OVER MUCH OF THE AREA.  
 
FRACASSO  
 
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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