979  
FXUS02 KWBC 081521  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1120 AM EDT WED AUG 08 2018  
 
VALID 12Z SAT AUG 11 2018 - 12Z WED AUG 15 2018  
   
..PATTERN OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
MODELS AND ENSEMBLES NOW SHOW BETTER THAN NORMAL CLUSTERING  
THROUGH THE PERIOD FOR THE CONUS, BOLSTERING FORECAST CONFIDENCE.  
THE PATTERN OFFERS AN EASTERN PACIFIC UPPER LOW THAT MOVES THROUGH  
SOUTHERN BRITISH COLUMBIA SATURDAY AS A LEAD UPPER LOW SINKS  
SLOWLY SOUTHWARD INTO THE OHIO VALLEY AND CLOSES OFF. SUBSEQUENT  
CANADIAN SYSTEM APPROACH TOWARD THE GREAT LAKES EARLY NEXT WEEK  
KICKS THE LEAD MIDWEST SYSTEM INTO NEW ENGLAND. THE WPC MEDIUM  
RANGE PRODUCT SUITE WAS MAINLY DERIVED FROM THE 00/06 UTC GFS AND  
00 UTC ECMWF ALONG WITH THEIR WELL PAIRED RESPECTIVE ENSEMBLE  
MEANS AND WPC CONTINUITY.  
   
..WEATHER HIGHLIGHTS AND HAZARDS
 
 
NEAR OR ABOVE RECORD HIGH TEMPERATURES OVER THE INTERIOR  
NORTHWEST/NORTHERN ROCKIES/HIGH PLAINS SATURDAY WILL TREND COOLER  
SUNDAY/MONDAY AS THE UPPER TROUGH AND SURFACE COLD FRONT PUSH  
THROUGH. A SEPARATED SOUTHWESTWARD EXTENSION FROM THE OH VALLEY  
UPPER TROUGH BY SUNDAY/MONDAY WILL HELP FUEL ORGANIZED RAIN/STORMS  
ACROSS TEXAS WESTWARD TO THE FOUR CORNERS REGION, ESPECIALLY NM/CO  
JUST TO THE EAST OF THE UPPER HIGH IN A REGION OF FAVORABLE UPPER  
DIFFLUENCE. GUIDANCE CONTINUES TO WAVER ON PLACEMENT BUT SEVERAL  
INCHES OF RAIN ARE LIKELY OVER CENTRAL TEXAS DURING THE SAT-WED  
TIME PERIOD.  
 
A WAVY FRONT WILL LINGER ACROSS THE U.S. SOUTHERN TIER DURING THE  
PERIOD WHICH WILL HELP SPARK AFTERNOON SHOWERS/STORMS AND LOCALLY  
HEAVY RAINFALL IN THE WARM/HUMID AIRMASS. AS THE UPPER TROUGH  
(EVENTUAL CLOSED LOW) DIGS/SHARPENS OVER THE EAST-CENTRAL U.S.,  
MORE WIDESPREAD PRECIPITATION MAY BE FAVORED TO ITS EAST ALONG THE  
APPALACHIANS TO THE I-95 CORRIDOR. THIS COULD DEVELOP INTO A MORE  
WIDESPREAD HEAVY RAINFALL THREAT CONSIDERING SLOW SYSTEM  
TRANSLATION AND AMPLITUDE WITH A SOUTHERLY FETCH OF AMPLE MOISTURE  
OVER SEVERAL DAYS. CLOSED LOWS IN THE SUMMER CAN BE UNDERESTIMATED  
IN THE SHORT AND MEDIUM RANGE IN TERMS OF PRECIPITATION  
INTENSITY/AMOUNTS AND LONGEVITY.  
 
UPSTREAM, AN APPROACHING FRONTAL BOUNDARY OVER THE HIGH  
PLAINS/UPPER MIDWEST/GREAT LAKES NEXT WEEK WILL ACT AS ANOTHER  
FOCUS FOR SHOWER/STORMS JUST TO ITS SOUTH AS THE LEFTOVER WEAKNESS  
ALOFT GETS ABSORBED INTO THE NEXT TROUGH.  
 
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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