338  
FXUS02 KWBC 131600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1200 PM EDT THU SEP 13 2018  
 
VALID 12Z SUN SEP 16 2018 - 12Z THU SEP 20 2018  
 
...DANGEROUS HURRICANE FLORENCE TO BRING CATASTROPHIC FLASH  
FLOODING AND PROLONGED SIGNIFICANT RIVER FLOODING TO PARTS OF THE  
CAROLINAS AND APPALACHIANS INTO NEXT WEEK...  
 
   
..HURRICANE FLORENCE
 
 
THE NATIONAL HURRICANE CENTER FORECASTS FLORENCE TO MAKE LANDFALL  
INTO NORTH CAROLINA FRIDAY MORNING. A WEAKENING FLORENCE SHOULD  
ARC THROUGH SOUTH CAROLINA BEFORE LIFTING ROUGHLY ALONG THE LENGTH  
OF THE APPALACHIANS SUNDAY-WEDNESDAY. THE MAIN THREAT FROM HEAVY  
AND PERSISTENT RAINFALL FOR FLOODING WILL REMAIN AS IT INTERACTS  
WITH APPALACHIAN TERRAIN. MUCH OF THE RAIN WILL FALL BEFORE THE  
MEDIUM RANGE PERIOD BEGINS, BUT A SIGNIFICANT AREA OF RAIN WILL  
FOLLOW MAINLY ALONG AND TO THE EAST OF THE APPALACHIANS NEXT WEEK.  
THIS WILL BE A MULTI-DAY AND MULTI-FACETED EVENT. PLEASE CONSULT  
THE NATIONAL HURRICANE CENTER AND YOUR LOCAL NWS FORECAST OFFICE  
FOR THE LATEST INFORMATION.  
   
..PATTERN OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
THE 00 UTC NAEFS/ECMWF ENSEMBLE MEANS WERE USED AS A STARTING  
POINT FOR WPC SURFACE FRONTS/PRESSURES PROGS DAYS 3-5 IN A PERIOD  
OF SMALLER FORECAST SPREAD EXCLUDING FLORENCE. THIS BLEND LEFT  
ROOM FOR INSERTION OF FLORENCE AS PER THE LATEST NHC FORECAST THAT  
DID NOT EXPLICITLY MATCH ANY PARTICULAR DETERMINISTIC MODEL.  
 
LATER, THE UPPER PATTERN FROM THE PACIFIC ACROSS NORTH AMERICA  
WILL MOSTLY REMAIN STAGNANT WITH MEANDERING RIDGING FROM SOUTHWEST  
ALASKA TO THE ALEUTIANS. THIS MAINTAINS A TROUGH POSITION TO ITS  
SOUTHEAST DOWN TOWARD THE PACIFIC NORTHWEST. THERE REMAINS  
DIFFERENCES CONCERNING TROUGHING NEXT WEDNESDAY/THURSDAY INTO THE  
NORTHWESTERN U.S. THE SOMEWHAT MORE AMPLIFIED ECMWF ENSEMBLES SEEM  
MORE REASONABLE THAN THE MORE PROGRESSIVE GEFS SOLUTIONS GIVEN  
UPSTREAM FLOW AMPLITUDE AND WPC CONTINUITY.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
FLORENCE WILL SPREAD A LARGE AREA OF SIGNIFICANT RAINFALL  
NORTHEASTWARD NEXT WEEK DESPITE ITS ACCELERATION AHEAD OF AN  
APPROACHING COLD FRONT. FLOODING MAY BE A CONCERN ALONG THE I-81  
TO I-95 CORRIDORS BUT WILL BE A FUNCTION OF FORWARD SPEED. BACK TO  
THE WEST, AS TROUGHING FINALLY MOVES OUT OF THE NORTHWEST, A COLD  
FRONT WILL USHER IN COOLER FALL AIR TO THE HIGH PLAINS AND UPPER  
MIDWEST/GREAT LAKES TUE-WED AND THEN TO THE EAST COAST NEXT  
THURSDAY AS EX-FLORENCE SHOULD RACE WELL INTO ATLANTIC CANADA  
THEN.  
EXPECT SOME RECORD HIGH MINIMUM TEMPERATURES ALONG/AHEAD OF THE  
MOIST TRACK OF FLORENCE.  
 
DEEPENING TROPICAL MOISTURE OVER THE GULF OF MEXICO AND EXPECTED  
TRACK OF A TROPICAL WAVE INTO SOUTHERN TEXAS AND THE RIO GRANDE  
VALLEY WILL MEANWHILE OFFER A THREAT OF LOCALLY HEAVY RAINFALL FOR  
THE AREA FROM THE WEEKEND INTO EARLY NEXT WEEK.  
 
MEANHWILE, A NEW AREA OF PRECIPITATION WILL TAKE SHAPE AND EXPAND  
OVER THE NORTHERN PLAINS AND UPPER MIDWEST NEXT WEEK AS WAVES AND  
ATTENDANT PRECIPTATION FOCUS ALONG/NEAR THE FRONT EXITS THE  
FOOTHILLS OF THE ROCKIES.  
 
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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