044  
FXUS02 KWBC 240700  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
300 AM EDT FRI AUG 24 2018  
 
VALID 12Z MON AUG 27 2018 - 12Z FRI AUG 31 2018  
   
..PATTERN OVERVIEW AND WEATHER HIGHLIGHTS/HAZARDS
 
 
AMPLIFIED MID-UPPER LEVEL TROUGHING OVER THE NORTH-CENTRAL ROCKIES  
AND INTERMOUNTAIN WEST MONDAY WILL TREK ENEWD OVER THE N-CENTRAL  
U.S. THEN EASTERN CANADA/NORTHEAST TUESDAY-THURSDAY. THIS WILL  
SUPPORT A WAVY/COOLING FRONTAL SYSTEM UNDERNEATH TO FOCUS  
LINGERING PERIODS OF ORGANIZED CONVECTION EXPECTED TO BE HEAVIEST  
FROM THE MID MISSISSIPPI VALLEY AND MIDWEST/GREAT LAKES ONWARD,  
BUT ALSO WORKING WITH LESS PREDICTABLE IMPULSE SUPPORT FARTHER  
SOUTH INTO DEEPENED MOSITURE AND INSTABILITY WITHIN A SUMMER TIME  
HOT SECTOR. SOME OF THESE CONVECTIVE DOWNPOURS WILL PRODUCE LOCAL  
RUNOFF ISSUES WITH REPEAT/TRAINING OF CELLS. UPSTREAM, A STRONG  
UPPER HIGH SOUTH OF THE GULF OF ALASKA WILL RETROGRADE AND ALLOW  
COOLING TROUGH POSITION REINFORCEMENT INTO/OFFSHORE THE PACIFIC  
NORTHWEST MID-LATE NEXT WEEK WITH ENOUGH FLOW TO INITIATE SOME  
PRECIPITATION.  
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
MODELS AND ENSEMBLES SHOW A SIMILAR LARGER SCALE PATTERN IN THE  
3-5 DAY PERIOD, BUT DIFFERENCES ARE PROBLEMATIC WITH SMALLER SCALE  
IMPULSES AND LOWER ATMOSPHERIC FOCUS TO DRIVE CONVECTION.  
ADDRESSED THIS WITH A BLEND OF THE GFS/ECMWF, GFS/ECMWF ENSEMBLES  
AND WPC CONTINUITY. FORECAST SPREAD INCREASES ENOUGH INTO DAYS 6/7  
TO RELY MAINLY ON GEFS/ECMWF ENSEMBLES AND STATISTICAL/BIAS  
CORRECTED GUIDANCE. SYSTEMS MOVING TO THE EASTERN PACIFIC AND  
LOWER 48 IN THIS PATTERN MAY FAVOR THE AMPIFIED SIDE OF THE  
SOLUTION ENVELOPE DUE TO DOWNSTREAM RIPPLE EFFECTS FROM THE  
ENTRAINMENT OF EXTRATROPICAL LOWS ASSOCIATED WITH CURRENT WEST  
PACIFIC TROPICAL SYSTEMS CIMARON AND SOULIK TOWARD ALASKA.  
 
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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