499  
FXUS02 KWBC 280647  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
246 AM EDT TUE AUG 28 2018  
 
VALID 12Z FRI AUG 31 2018 - 12Z TUE SEP 04 2018  
 
...GUIDANCE/PREDICTABILITY ASSESSMENT AND WEATHER  
HIGHLIGHTS/HAZARDS...  
 
IT REMAINS THE CASE THAT A SERIES OF SHORTWAVE TROUGHS OF  
UNCERTAIN AMPLITUDE WILL DIG OVER THE NORTHEASTERN PACIFIC AND  
SPLIT OFF THE WEST COAST, WITH MORE ENERGETIC FLOW AND MODEST  
PRECIPITATION POTENTIAL ACROSS THE NORTHWESTERN U.S. TO THEN  
PROGRESS 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 TO  
THE GREAT LAKES/OHIO VALLEY/MID-ATLANTIC. MEANWHILE, INCREASING  
POTENTIAL FOR PACIFIC ENERGY TO WORK INLAND IN SEPARATED OR  
BROADER SOUTHERN STREAM FLOW NEXT WEEKEND/EARLY NEXT WEEK MAY  
RENEW MONSOONAL CONNECTIONS OVER THE SOUTHWEST AND SOUTH-CENTRAL  
GREAT BASIN/ROCKIES.  
 
MEANWHILE EXPECT A THREAT FOR LOCALLY EXCESSIVE, BUT LESS  
ORGANIZED THUNDERSTORMS/HEAVY DOWNPOURS IN THE HOT/HUMID SECTOR IN  
THE SOUTHERN/EASTERN U.S. WHICH MAY ALIGN WITH MESO-BOUNDARIES AND  
LOCAL CONVERGENCE EFFECTS. THERE IS ALSO POTENTIAL FOR HEAVY  
RAINFALL OVER FLORIDA AND ALONG THE GULF COAST AS PER WPC/NHC  
COORDINATED TROPICAL WAVE PASSAGE.  
 
OVERALL, MODELS AND ENSEMBLES SHOW ABOVE AVERAGE FORECAST SPREAD  
INTO THE LOWER 48 MANIFESTED MAINLY FROM UNCERTAIN FLOW EVOLUTIONS  
UPSTREAM OVER THE PACIFIC. THIS MAY IN PART BE DUE TO UPSTREAM  
TROPICAL SYSTEM FLOW ENTRAINMENTS AND ASSOCIATED RIPPLE EFFECTS.  
THIS IS RESULTING IN AMPLE RUN TO RUN FLIP FLOPPING WITH EVEN  
ENSEMBLE MEANS SHOWING UNCHARACTERISTIC VARIANCE. THE WPC MEDIUM  
RANGE PRODUCT SUITE USED A COMPOSITE SOLUTION.  
 
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  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page