288  
FXUS02 KWBC 151600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1200 PM EDT SAT SEP 15 2018  
 
VALID 12Z TUE SEP 18 2018 - 12Z SAT SEP 22 2018  
   
..PATTERN OVERVIEW AND WEATHER HIGHLIGHTS/HAZARDS
 
 
THE MEDIUM RANGE FORECAST PERIOD BEGINS TUESDAY WITH A TROUGH  
CENTERED NEAR THE WEST COAST, AN UPPER LEVEL RIDGE OVER THE  
SOUTH-CENTRAL U.S., AND A MID-UPPER LEVEL TROUGH OVER THE  
APPALACHIANS. THIS TROUGH FORCES THE POST-TROPICAL REMNANTS OF  
FLORENCE TO EJECT ALONG WITH A LEAD SWATH OF HEAVY RAINFALL ACROSS  
THE NORTHEASTERN STATES TO THEN DEEPEN OFFSHORE INTO THE CANADIAN  
MARITIMES AND NORTHERN ATLANTIC. THE SOUTH-CENTRAL U.S. UPPER  
RIDGE SHIFTS TO THE SOUTHEAST STATES LATER WEEK AS FLOW FROM THE  
ROCKIES TO THE NORTHEAST FLATTENS AS A SERIES OF IMPULSES PROGRESS  
EASTWARD OVER THE U.S. NORTHERN TIER IN THE WAKE OF FLORENCE. THIS  
FORCES A WAVY COLD FRONT DOWN THROUGH THE MID-LATITUDES THAT  
UPSTREAM COMBINES WITH GULF OF MEXICO RETURN INFLOW AND DYNAMIC  
UPPER SUPPORT TO FOCUS DEVELOPMENT OF AN INCREASINGLY WIDESPREAD  
NORTH-CENTRAL U.S. HEAVY RAINFALL PATTERN INTO MID-LATE WEEK AND  
AMPLE POST-FRONTAL COOLING. UNDERNEATH, THERE IS ALSO INDICATION  
SOME INFLUX OF EASTERN PACIFIC AND GULF OF MEXICO SOURCED TROPICAL  
MOISTURE MAY WORK ACROSS MEXICO TO FUEL INCREASED RAINFALL  
POTENTIAL INFRINGING INTO THE SOUTHWEST U.S. LATE WEEK.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
BEYOND FLORENCE, THERE IS DECENT LARGE SCALE PATTERN AGREEMENT IN  
THE PREFERRED ENSEMBLE MEANS, WITH THE GREATEST DIFFERENCES NOTED  
IN INDIVIDUAL RUNS/MODELS WITH THE EVOLVING MID-UPPER LEVEL TROUGH  
NEAR THE WEST COAST AND THE TIMING/AMPLITUDE OF SHORTWAVES  
EJECTING OVER THE U.S. NORTHERN TIER.  
 
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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