403  
FXUS02 KWBC 271610  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1210 PM EDT MON AUG 27 2018  
 
VALID 12Z THU AUG 30 2018 - 12Z MON SEP 03 2018  
   
..GUIDANCE AND UNCERTAINTY ASSESSMENT
 
 
MODEL GUIDANCE THIS MORNING SHOWS REASONABLY GOOD AGREEMENT ON THE  
OVERALL SYNOPTIC PATTERN EVOLUTION ACROSS THE U.S. THROUGH THE  
MEDIUM RANGE PERIOD. A HIGH PRESSURE RIDGE SHOULD CONTINUE TO BE  
MORE DOMINANT FROM THE CENTRAL U.S. TO THE EAST COAST THROUGH THE  
LABOR DAY WEEKEND AS A SHORTWAVE TROUGH MOVES ACROSS THE NORTHERN  
PLAINS. MEANWHILE, A SPLIT FLOW IS DEPICTED FOR THE WESTERN U.S.  
WITH THE NORTHERN STREAM SHOWING A TENDENCY FOR AMPLIFICATION OVER  
THE PACIFIC NORTHWEST INTO THE NORTHERN ROCKIES WHILE A SHORTWAVE  
IN THE SOUTHERN STREAM MOVES INTO CALIFORNIA. DETERMINISTIC MODEL  
SOLUTIONS AGREE QUITE WELL THROUGH DAY 5 SATURDAY AND A COMPROMISE  
BETWEEN THE 06Z GFS AND 00Z ECMWF YIELDS GOOD CONTINUITY WITH THE  
PREVIOUS WPC PACKAGE. FOR DAYS 6 AND 7, THE DETERMINISTIC ECMWF  
HAS BEEN SLOWING DOWN THE EASTWARD PROGRESSION OF THE FRONT/TROUGH  
ACROSS THE NORTHERN TIER AND APPEARS TO CONVERGE TOWARD A SOLUTION  
FOR SURFACE CYCLOGENESIS OVER THE NORTHERN HIGH PLAINS INTO  
ALBERTA CANADA BY LABOR DAY. THE GFS HAS BEEN A LITTLE MORE  
CONSISTENT ON SHOWING CYCLOGENESIS IN THAT VICINITY. THEREFORE,  
MORE OF THE ENSEMBLE MEANS FROM THE 00Z EC AND 06Z GEFS WITH A  
SLIGHT PREFERENCE TOWARD THE 06Z GEFS FOR THE DAY 6 AND 7  
SEA-LEVEL PRESSURE FIELD.  
   
..WEATHER PATTERN HIGHLIGHTS AND HAZARDS
 
 
A CONTINUING SERIES OF SHORTWAVE TROUGHS WILL DIG OVER THE  
NORTHEASTERN PACIFIC AND SPLIT OFF THE WEST COAST, BUT WITH MORE  
ENERGETIC FLOW AND MODEST PRECIPITATION POTENTIAL ACROSS THE  
NORTHWESTERN U.S., THEN PROGRESSING EAST-NORTHEASTWARD THROUGH  
SOUTHERN CANADA AND THE U.S. NORTHERN TIER. WAVY FRONTAL SYSTEMS  
UNDERNEATH WILL COMBINE WITH DEEPENED MOISTURE AND INSTABILITY TO  
FUEL PERIODS OF HEAVY CONVECTION, FOCUSED FROM THE EASTERN  
PLAINS/MISSISSIPPI VALLEY AND MID-SOUTH TO THE GREAT LAKES/OHIO  
VALLEY/MID-ATLANTIC. MEANWHILE, THE POTENTIAL FOR SOME PACIFIC  
ENERGY TO EVENTUALLY WORK INLAND IN SEPARATED SOUTHERN STREAM FLOW  
BY NEXT WEEKEND MAY RENEW MONSOONAL CONNECTIONS OVER THE SOUTHWEST  
AND SOUTH-CENTRAL GREAT BASIN/ROCKIES.  
 
EXPECT A THREAT FOR LOCALLY EXCESSIVE, BUT LESS ORGANIZED,  
THUNDERSTORMS/HEAVY DOWNPOURS WITHIN THE HOT/HUMID SECTOR IN THE  
SOUTHERN/EASTERN U.S. WHICH MAY ALIGN WITH MESO-BOUNDARIES AND  
LOCAL CONVERGENCE EFFECTS. THIS POTENT LATE SUMMER HOT SECTOR  
UNDER RIDGING ALOFT WILL OFFER LINGERING WIDESPREAD RECORD HIGH  
MINIMUM TEMPERATURES INTO THURSDAY WITH HIGH DEW POINTS INTO THE  
UPPER 60S AND LOW 70S. A MODERATING FRONT WILL PUSH THROUGH THE  
NORTHEAST AND THE MID-ATLANTIC THEREAFTER, SETTLING THROUGH THE  
CAROLINAS. THE HOT SECTOR OVER THE U.S. SOUTHERN TIER WILL  
GENERALLY HOLD FIRM THIS WEEK.  
 
KONG/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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