246  
FXUS02 KWBC 210700  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
300 AM EDT WED AUG 21 2024  
 
VALID 12Z SAT AUG 24 2024 - 12Z WED AUG 28 2024  
   
..HAZARDOUS HEAT FOCUS OVER THE SOUTHERN PLAINS
 
 
   
..OVERVIEW
 
 
A PERSISTENT AND AMPLIFIED UPPER PATTERN OVER OUR NATION REMAINS  
HIGHLIGHTED BY A RIDGE EXPANDING FROM THE SOUTHERN PLAINS, COOLING  
TROUGHING OVER THE NORTHEAST/EAST, AND A TROUGH/LOW EJECTING  
INLAND IN A WET PATTERN OVER THE NORTHWEST THEN NORTH-CENTRAL U.S.  
THIS WEEKEND INTO NEXT WEEK. THIS PATTERN OFFERS A HAZARDOUS HEAT  
FOCUS OVER TEXAS, MOIST MONSOONAL FLOW LINGEIRNG INTO THE WEEKEND  
OVER THE FOUR CORNERS STATES, COOLED SURFACE HIGH PRESSURE ALONG  
THE EASTERN SEABOARD AND TROPICAL MOISTURE LURKING NEAR THE GULF  
COAST AND ESPCIALLY ACROSS SOUTH FLORIDA.  
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
IN A NEAR REPEAT OF TRENDS INHERENT TO THE LAST FEW DAYS WORTH OF  
MODEL AND ENSEMBLE FORECASTS, DIFFERENCES LINGER WITH THE HANDLING  
OF DEEP EASTERN PACIFIC UPPER TROUGH/LOW ENERGY INLAND ACROSS THE  
WEST/NORTHWEST THIS WEEKEND. RECENT 06/18 UTC GFS RUNS AND TO SOME  
EXTENT 06/18 UTC GEFS RUNS HAVE BEEN PRONE TO FAVOR A SOLUTION ON  
THE MORE PROGRESSIVE SIDE OF GUIDANCE, WHILE MOST OTHER GUIDANCE  
HAS BEEN ON THE SLOWER SIDE OF THE FULL ENVELOPE OF SOLUTIONS WITH  
RECENT RUNS, INCLUDING MANY 00/12 UTC GFS/GEFS RUNS. THE MANUALLY  
OVERSEEN FORECAST FROM HERE AT WPC HAS TRIED TO BE CONSISTENT IN  
FAVORING THE LESS PROGRESSIVE PATTERN CAMP. TODAY IS NO EXCEPTION.  
 
IN THIS VEIN, A COMPOSITE OF BEST CLUSTERED GUIDANCE FROM THE 12  
UTC ECMWF/CANADIAN AND ECMWF ENSEMBLE MEAN WAS PRIMARILY USED TO  
DERIVE THE WPC MEDIUM RANGE PRODUCT SUITE FROM THIS WEEKEND INTO  
NEXT MIDWEEK IN CONJUCTURE WITH THE 01 UTC NATIONAL BLEND OF  
MODELS AND WPC PRODUCT CONTINUITY.  
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
UPPER TROUGH AMPLIFICATION PROXIMITY ALONG/OFF THE WEST COAST  
PORTENDS A COOLER AND WETTER PATTERN FOR THE NORTHWEST. RAINS AND  
SPOTTY HIGH ELEVATION MOUNTAIN SNOWS MAY WORK INLAND ACROSS THE  
NORTH-CENTRAL INTERMOUNTAIN WEST/ROCKIES THIS WEEKEND INTO EARLY  
NEXT WEEK DEPENDENT ON THE TRACK/TIMING OF THE SUPPORTING UPPER  
TROUGH/LOW EJECTION. THERE'S POTENTIAL FOR ENHANCED RAINFALL  
AMOUNTS ASSOCIATED WITH CONVECTION. RAINS/CONVECTION MAY ALSO  
CONSOLIDATE DOWNSTREAM OVER THE NORTH-CENTRAL U.S. EARLY NEXT WEEK  
GIVEN FOCUS FROM POSSIBLE MODERATE CYCLOGENESIS/FRONTOGENESIS.  
 
MEANWHILE, A MONSOONAL CONVECTIVE PATTERN WILL LINGER BUT  
GRADUALLY EASE OVER THE SOUTHWEST/FOUR CORNERS INTO SATURDAY WITH  
MOIST SOUTHERLY FLOW WEST OF A SLOW TO DISLODGE UPPER RIDGE AXIS  
CENTERED OVER THE SOUTHERN PLAINS. SOME MOISTURE MAY BE PULLED  
NORTHWARD INTO THE NORTHERN INTERMOUNTAIN WEST/ROCKIES THIS WEEKEND  
AHEAD OF PACIFIC UPPER TROUGH/LOW TRANSLATION OVER THAT REGION.  
THE WPC DAY 4/5 EXCESSIVE RAINFALL OUTLOOKS FOR SATURDAY/SUNDAY  
SHOW MARGINAL RISK AREAS. LOCAL STORMS WITH EMBEDDED HEAVY RAIN  
MAY CAUSE FLASH FLOODING, PARTICULARLY IN VULNERABLE AREAS.  
 
UPPER RIDGING FOCUS OVER THE SOUTH-CENTRAL U.S. WILL SUPPORT 5-15  
DEGREE ABOVE NORMAL TEMPERATURES. HIGHS WELL INTO THE 100S IN MUCH  
OF TEXAS IN PARTICULAR COULD SET DAILY RECORDS AND HIGH DEWPOINTS  
SHOULD PRODUCE HEAT INDICES LIKELY ABOVE 110 DEGREES. LOW  
TEMPERATURES IN THE UPPER 70S TO LOW 80S WILL EXACERBATE HEAT  
STRESS AND COULD SET RECORDS FOR WARM MINIMUM TEMPERATURES.  
EXPERIMENTAL HEATRISK CONTINUES TO INDICATE MAJOR TO EXTREME  
IMPACTS FROM THIS HEAT. THIS WILL BE IN CONTRAST TO COOLING  
CONDITIONS INTO THE WEST/NORTHWEST AND ALSO OVER THE CENTRAL TO  
EASTERN U.S. UNDER THE INFLUENCE OF DAMMED SURFACE HIGH PRESSURE.  
SOME RECORD COOL OVERNIGHT TEMPERATURE VALUES ARE POSSIBLE OVER THE  
EAST IN THIS PATTERN INTO LATER WEEK, BUT EXPECT SUMMER HEAT TO  
THEN STEADILY RETURN WITH SPREAD ACROSS THE CENTRAL-EASTERN U.S..  
 
ELSEWHERE, A TRAILING FRONT STALLING ACROSS FLORIDA WILL MAINTAIN  
PERIODIC RAIN/THUNDERSTORM CHANCES THERE AND INTO SOUTHEAST U.S.  
COASTAL AREAS LATER WEEK INTO NEXT WEEK. MOIST FLOW AND PATTERN  
LONGEVITY MAY LEAD TO POSSIBLE FLOODING ISSUES, ESPECIALLY IF HEAVY  
RAIN FALLS IN URBAN AREAS. WPC DAY4/5 WEEKEND ERO MARIGINAL RISK  
AREA WAS INTRODUCED FOR SOUTH FLORIDA GIVEN MOISTURE.  
 
SCHICHTEL  
 
ADDITIONAL 3-7 DAY HAZARD INFORMATION CAN BE FOUND ON THE WPC MEDIUM  
RANGE HAZARDS OUTLOOK CHART AT:  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP  
 
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION FORECAST (QPF), EXCESSIVE RAINFALL  
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT  
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:  
 
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/#PAGE=ERO  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW  
 

 
 
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