996  
FXUS02 KWBC 290659  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
258 AM EDT WED AUG 29 2018  
 
VALID 12Z SAT SEP 01 2018 - 12Z WED SEP 05 2018  
 
...GUIDANCE/PREDICTABILITY ASSESSMENT AND WEATHER  
HIGHLIGHTS/HAZARDS...  
 
STREAM SPLIT SHORTWAVE TROUGHS OF UNCERTAIN AMPLITUDE/TIMINGS WILL  
CONTINUE TO FEED INTO WESTERN NORTH AMERICA. EXPECT AN ENERGETIC  
STREAM FLOW TO DRIVE MODEST PRECIPITATION OVER THE NORTHWESTERN  
U.S. THEN MORE IN ERNEST THROUGH THE NORTH-CENTRAL AND TO A LESSER  
EXTENT THE EASTERN U.S. WAVY FRONTAL SYSTEMS COMBINE WITH THETA-E  
ADVECTION/DEEPENED MOISTURE/INSTABILITY TO FUEL PERIODS OF HEAVY  
CONVECTION/MCS ACTIVITY FOCUSING FROM THE EASTERN  
PLAINS/MISSISSIPPI VALLEY. ADDITIONAL CONVECTION MAY SPREAD INTO  
THE GREAT LAKES/OHIO VALLEY/MID-ATLANTIC. MEANWHILE, INCREASING  
POTENTIAL FOR PACIFIC ENERGIES TO WORK INLAND IN SEPARATED OR  
BROADER SOUTHERN STREAM FLOW ARE EXPECTED TO RENEW SOME MONSOONAL  
CONNECTIONS/CONVECTION FOR 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. HOWEVER, THERE ARE ALSO SEVERAL SYSTEMS  
OF OPPORTUNITY FOR HEAVY RAINFALL OVER FLORIDA AND ALONG THE GULF  
COAST WITH APPROACH AND PASSAGE OF TWO DEEPLY MOIST TROPICAL WAVES  
BEING FOLLOWED/COORDINATED BY WPC AND NHC.  
 
OVERALL, MODELS AND ENSEMBLES STILL SHOW ABOVE NORMAL FORECAST  
SPREAD INTO THE LOWER 48 MANIFESTED MAINLY FROM UNCERTAIN FLOW  
EVOLUTIONS UPSTREAM OVER THE PACIFIC. THIS MAY IN PART BE DUE TO  
MULTIPLE UPSTREAM X-TROPICAL SYSTEM FLOW ENTRAINMENTS AND RIPPLE  
EFFECTS ALONG WITH UNCERTAIN MULTIPLE FLOW STREAM  
INTERACTIONS/SEPARATIONS INTO NORTH AMERICA. THIS IS RESULTING IN  
AMPLE RUN TO RUN FLIP FLOPPING WITH EVEN ENSEMBLE MEANS SHOWING  
UNCHARACTERISTIC VARIANCE. ACCORDINGLY, THE WPC MEDIUM RANGE  
PRODUCT SUITE WAS PRIMARILY DERIVED FROM A COMPOSITE BLEND OF  
LATEST ENSEMBLE MEANS AND NBM/WPC CONTINUITY. ALTHOUGH OVERALL  
LATE SUMMER PATTERN DETAILS/TIMINGS REMAIN UNRESOLVED, THE MAIN  
FOCUS REGIONS FOR HEAVIER ORGANIZED PRECIPITATION ARE SIMILARILY  
SUGGESTED BY THE BULK OF GUIDANCE.  
 
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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