553  
FXUS02 KWBC 281606  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1205 PM EDT TUE AUG 28 2018  
 
VALID 12Z FRI AUG 31 2018 - 12Z TUE SEP 04 2018  
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
MODEL GUIDANCE CONTINUES TO BE IN GOOD AGREEMENT WITH THE OVERALL  
SYNOPTIC PATTERN ACROSS THE U.S. THROUGH THE MEDIUM RANGE PERIOD.  
THE UPPER RIDGE WILL REMAIN THE DOMINANT FEATURE ACROSS THE  
CENTRAL U.S., SOUTHEAST AND EAST COAST. MEANWHILE, MODEL GUIDANCE  
CONTINUES TO SHOW AN AMPLIFIED TROUGH OVER THE PACIFIC NORTHWEST  
AND NORTHERN ROCKIES. THIS TROUGH WILL SLIDE EASTWARD TOWARD THE  
U.S. NORTHERN TIER LATER IN THE MEDIUM RANGE PERIOD. MEANWHILE,  
PACIFIC ENERGY WILL MOVE INLAND ACROSS CALIFORNIA--EITHER IN  
SEPARATE OR BROADER SOUTHERN STREAM FLOW BY LATE THIS WEEKEND AND  
INTO EARLY NEXT WEEK. MODEL GUIDANCE STILL NEEDS TO RESOLVE THE  
EVOLUTION OF THIS ENERGY--ALTHOUGH THE 00Z NAEFS/00Z ECMWF AND THE  
06Z GEFS SHOW A TROUGH OVER THE WEST COAST BY DAY 5 BUT DETAILS  
ARE SLIGHTLY DIFFERENT. THE 00Z NAEFS/00Z ECMWF ARE ALSO IN  
AGREEMENT IN DAY 6/7 A TROUGH OVER THE WEST COAST SLIDING OVER THE  
INTERMOUNTAIN WEST/NORTHERN PLAINS. WPC USED A BLEND OF THE 00Z  
CMC/ECMWF AND 06Z GFS IN THE BEGINNING OF THE MEDIUM RANGE PERIOD  
AND INCREASED THE USE OF THE 00Z NAEFS/00Z ECENS LATER IN THE  
PERIOD TO ACCOUNT FOR THE ABOVE AVERAGE FORECAST SPREAD ESPECIALLY  
FROM THE FLOW EVOLUTION UPSTREAM OVER THE PACIFIC.  
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
WITH MULTIPLE FRONTS MOVING INTO THE NORTHERN PLAINS AND UPPER  
MIDWEST--ALONG WITH A WAVY FRONT DRAPED ACROSS THE OHIO VALLEY AND  
MID-ATLANTIC, DEEPENED MOISTURE AND INSTABILITY WILL FUEL PERIODS  
OF HEAVY RAINFALL ESPECIALLY ACROSS THE MIDDLE/UPPER MISSISSIPPI  
VALLEY, GREAT LAKES, OHIO VALLEY AND MID-ATLANTIC IN THE BEGINNING  
OF THE MEDIUM RANGE PERIOD. AS THE NEXT ROUND OF HEAVY RAINFALL  
WILL BE EXPECTED FOR THE NORTHERN PLAINS AND UPPER MIDWEST LATER  
IN THE MEDIUM RANGE PERIOD AS ANOTHER ROUND OF FRONTS MOVE ACROSS  
THESE REGIONS. FARTHER SOUTH, DIURNALLY DRIVEN THUNDERSTORMS  
ACROSS THE SOUTHEAST AND GULF COAST COULD BRING LOCALLY EXCESSIVE  
RAINFALL--BUT LESS ORGANIZED THUNDERSTORMS. A TROPICAL WAVE  
PASSAGE OVER FLORIDA AND INTO THE GULF OF MEXICO COULD BRING A  
POTENTIAL OF HEAVY RAINFALL TO THE STATE AND ACROSS THE GULF  
COAST.  
 
REINHART/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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