750  
FXUS02 KWBC 270654  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
253 AM EDT MON AUG 27 2018  
 
VALID 12Z THU AUG 30 2018 - 12Z MON SEP 03 2018  
   
..WEATHER PATTERN HIGHLIGHTS AND HAZARDS
 
 
A CONTINUING SERIES OF SHORTWAVE TROUGHS WILL DIG OVER THE  
NORTHEASTERN PACIFIC TO 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.  
 
   
..GUIDANCE AND UNCERTAINTY ASSESSMENT
 
 
THE LARGER SCALE FLOW PATTERN IS REASONABLY WELL DEPICTED IN  
GUIDANCE SO WHILE OVERALL WEATHER THREATS SEEM DOCUMENTED,  
DETERMINISTIC EFFORTS TO DETAIL MUCH LESS PREDICTABLE EMBEDDED  
FEATURES AND LOCAL FOCUS FOR CONVECTION HAVE BEEN SUFFERING FROM  
RUN TO RUN VARIANCE AND FLIP-FLOPPING. THAT SAID, THE LATEST GFS  
AND ECMWF RUNS HAVE CONVERGED A BIT MORE ON THEIR SOLUTIONS OVER  
MEDIUM RANGE TIME SCALES, BOLSTERING FORECAST CONFIDENCE A BIT.  
ACCORDINGLY, THE WPC MEDIUM RANGE PRODUCT SUITE WAS MAINLY DERIVED  
FROM A COMPOSITE BLEND OF ENSEMBLES, THE NATIONAL BLEND OF MODELS  
AND WPC CONTINUITY, WITH RAPIDLY DECREASING DETERMINITSIC MODEL  
INPUT DAYS 5-7 AMID GROWING UNCERTAINTIES.  
 
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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