436  
FXUS02 KWBC 111601  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1201 PM EDT SAT AUG 11 2018  
 
VALID 12Z TUE AUG 14 2018 - 12Z SAT AUG 18 2018  
   
..PATTERN OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
SEVERAL SLOW MOVING CUT-OFF UPPER LOWS WILL INITIALLY SITUATE OVER  
THE MID-ATLANTIC AND SOUTHERN/CENTRAL PLAINS, RESPECTIVELY. WITH  
THE EXITING CLOSED LOW OVER THE MID-ATLANTIC...WEAK UPSTREAM  
HEIGHT FALLS SHOULD EVENTUALLY NUDGE THE SYSTEM OFFSHORE IN THE  
FOLLOWING DAYS ENTERING THE CANADIAN MARITIMES BY LATE THURSDAY.  
SHIFTING FOCUS TO THE LONGWAVE TROUGH SITTING OVER THE GREAT LAKES  
AND POINTS SOUTHWARD, THERE IS PLENTY OF ENSEMBLE SPREAD WITH  
REGARDS TO PLACEMENT AND MAGNITUDE. ADDITIONALLY, RUN-TO-RUN  
CONTINUITY IS LACKING SUGGESTING FUTURE SHIFTS IN THE NEWER  
GUIDANCE. FARTHER UPSTREAM, MODELS REMAIN UNCERTAIN ON THE  
POLEWARD EXTENT OF RIDGING ACROSS WESTERN NORTH AMERICA LATE IN  
THE PERIOD. IT DOES APPEAR A 594-DM MID-LEVEL RIDGE WILL  
RE-ESTABLISH A SEMI-PERMANENT SUMMER HOME OVER THE DESERT  
SOUTHWEST.  
 
ACCORDINGLY, STARTED THE WPC FORECAST PROCESS WITH AN EVENLY  
WEIGHTED BLEND OF THE WELL CLUSTERED 00 UTC GFS/ECMWF AND 00 UTC  
GEFS/ECMWF ENSEMBLES DAY3/TUESDAY. WITH UNCERTAINTY BUILDING  
ACROSS MANY KEY FEATURES ON THE MAP, INCREASINGLY WEIGHTED  
ENSEMBLES OVER TIME THROUGH MEDIUM RANGE TIME SCALES AT THE  
EXPENSE OF DETERMINISTIC MODELS. BY EARLY NEXT WEEKEND, THIS  
BLENDED APPROACH STILL SUPPORTS A WEAK NEGATIVE HEIGHT ANOMALY  
ACROSS THE GREAT LAKES AND ITS VICINITY WHILE A MEAN RIDGE SETS UP  
ACROSS A LARGE CHUNK OF THE WESTERN U.S.  
   
..WEATHER HIGHLIGHTS AND HAZARDS
 
 
WET WEATHER IN STORE FOR THE SOUTHERN/CENTRAL PLAINS, AND MODELS  
SHOW SOME HEALTHY LOCAL DOWNPOURS. OTHERWISE, THERE WILL BE A  
DAILY CHANCE FOR THUNDERSTORMS ALMOST ANYWHERE EAST OF THE  
MISSISSIPPI RIVER GIVEN THE SLOW MOVING LONGWAVE TROUGH COMBINED  
WITH A ROBUST WARM SECTOR. ACROSS THE DESERT SOUTHWEST, MONSOONAL  
CONVECTION SHOULD BREAK OUT EACH AFTERNOON/EVENING. RECENT GFS  
RUNS HAVE SHOWN VERY HIGH AMOUNTS COMPARED TO MOST OTHER GUIDANCE,  
BUT THESE APPEAR CONTAMINATED BY CONVECTIVE FEEDBACK.  
 
RUBIN-OSTER/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  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page