549  
FXUS02 KWBC 251510  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1109 AM EDT SAT AUG 25 2018  
 
VALID 12Z TUE AUG 28 2018 - 12Z SAT SEP 01 2018  
   
..OVERVIEW AND GUIDANCE EVALUATION/PREFERENCES
 
 
LATEST GUIDANCE SHOWS A SIMILAR LARGER SCALE PATTERN NEXT WEEK AS  
UPPER RIDGING HOLDS OVER THE SOUTHEAST WITH SUCCESSIVE POSITIVELY  
TILTED TROUGHS INTO THE NORTHWEST. UPSTREAM EX-TROPICAL SYSTEMS  
SOULIK AND CIMARON WILL LIKELY AMPLIFY THE FLOW INTO THEN EAST OF  
THE BERING SEA (SEE PMDAK) ATOP A NORTH PACIFIC UPPER HIGH WHICH  
WILL ALLOW TROUGHING TO REMAIN FAVORED IN THE WEST. THE  
MODELS/ENSEMBLES HAVE WAVERED ON THE SPEED OF EXITING STRUNG OUT  
VORTICITY FEATURES FROM THE MEAN TROUGH POSITION BUT GIVEN SOME  
OSCILLATING VARIANCE BETWEEN MODEL CYCLES, A BLEND OF THE  
BEST-CLUSTERED SOLUTIONS WAS PRUDENT -- THIS INCLUDED THE 00Z  
FV3-GFS/ECMWF/CANADIAN AND THE 00Z GEFS/ECENS MEANS. UNCERTAINTY  
EXPANDS, AS EXPECTED, BY DAYS 6-7 IN THE EAST WITH THE SOUTHWARD  
EXTENT OF THE FRONT AND AREAS OF CONVECTION ALONG/AHEAD OF IT BACK  
THROUGH THE CENTRAL U.S.  
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
A WAVY FRONTAL SYSTEM ACROSS ROUGHLY THE NORTHERN HALF OF THE  
LOWER 48 WILL FOCUS PERIODS OF ORGANIZED CONVECTION ALONG IN A  
QUITE SUMMERY AIR MASS, ESPECIALLY EAST OF THE PLAINS. POTENTIALLY  
STRONG ACTIVITY SHOULD OCCUR FROM THE PLAINS AND MIDWEST/GREAT  
LAKES EASTWARD TUE-WED AHEAD OF THE COLD FRONT, THOUGH LOCATION  
PREDICTABILITY REMAINS LOW PER SPC. TO THE SOUTH, LESS PREDICTABLE  
MESOSCALE PROCESSES WITHIN THE HOT/HUMID SUMMERTIME AIRMASS  
(TEMPERATURES WELL ABOVE AVERAGE TO NEAR RECORD LEVELS, ESPECIALLY  
FOR MINIMUMS) AND DEEP MOISTURE/INSTABILITY WILL ALSO GIVE RISE TO  
LOCALLY HEAVY RAINFALL WHICH MAY PRODUCE LOCAL RUNOFF ISSUES WITH  
REPEAT/TRAINING OF CELLS. UPSTREAM, A STRONG UPPER HIGH SOUTH OF  
THE GULF OF ALASKA WILL RETROGRADE WESTWARD AND ALLOW ANOTHER  
COOLING TROUGH INTO THE PACIFIC NORTHWEST MID-LATE WEEK WITH  
ENOUGH ONSHORE FLOW TO INITIATE MODEST PRECIPITATION.  
 
FRACASSO/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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