092  
FXUS02 KWBC 250625  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
225 AM EDT SAT AUG 25 2018  
 
VALID 12Z TUE AUG 28 2018 - 12Z SAT SEP 01 2018  
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
GUIDANCE SHOWS A SIMILAR LARGER SCALE PATTERN HEADING INTO  
MIDWEEK, BUT SMALLER SCALE DIFFERENCES THAT WILL DRIVE CONVECTIVE  
EVOLUTIONS WILL REMAIN LESS RESOLVED UNTIL THE SHORT TERM. A MODEL  
AND ENSEMBLE COMPOSITE BLEND WAS SUITABLE FOR TUESDAY, BUT QUICKLY  
GROWING SYSTEM VARIANCE PORTENDS USE OF 12 UTC GEFS/ECMWF  
ENSEMBLES THEREAFTER. THESE PARTICULAR ENSEMBLE RUNS OFFER FLOW ON  
THE AMPLIFIED SIDE OF RECENT FULL SOLUTION ENVELOPES. DESPITE  
UNCERTAINTY WITH RUN TO RUN SOLUTION FLIPPING DIURNALLY OVER THE  
PAST FEW RUNS, AMPLIFICATION IS FAVORED DOWNSTREAM WITH RIPPLE  
EFFECTS FROM THE ENTRAINMENT OF EXTRATROPICAL LOWS ASSOCIATED WITH  
WEAKENING WEST PACIFIC TROPICAL SYSTEMS CIMARON AND SOULIK. THERE  
IS ALSO SOME UNCERTAINTY WITH THE SOUTHWARD EXTENT OF THE FRONT  
AND ASSOCIATED CONVECTION OVER THE CENTRAL AND EASTERN U.S. AS IT  
BATTLES UPPER RIDGING.  
   
..PATTERN OVERVIEW AND WEATHER HIGHLIGHTS/HAZARDS
 
 
A LEAD AMPLIFIED MID-UPPER LEVEL TROUGH IS EXPECTED TO PROGRESS  
EAST-NORTHEASTWARD OVER THE NORTH-CENTRAL U.S. THEN THROUGH THE  
NORTHEAST AND EASTERN CANADA TUESDAY-THURSDAY. THIS WILL SUPPORT  
THE SINKING OF A WAVY FRONTAL SYSTEM ACROSS ROUGHLY THE NORTHERN  
HALF OF THE LOWER 48 WHICH WILL FOCUS PERIODS OF ORGANIZED  
CONVECTION. POTENTIALLY STRONG ACTIVITY SHOULD OCCUR FROM THE  
SOUTH-CENTRAL PLAINS/MID-MISSISSIPPI VALLEY AND MIDWEST/GREAT  
LAKES EASTWARD. 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.  
 
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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