339  
FXUS02 KWBC 310640  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
239 AM EDT WED AUG 31 2022  
 
VALID 12Z SAT SEP 03 2022 - 12Z WED SEP 07 2022  
 
...PROLONGED AND DANGEROUS HEAT WAVE FOR PORTIONS OF THE WESTERN  
U.S. THROUGH THE HOLIDAY WEEKEND...  
 
...HEAVY RAIN THREAT FROM SOUTHERN/SOUTHEAST TEXAS THROUGH THE  
CENTRAL GULF COAST STATES...  
 
   
..OVERVIEW
 
 
A ANOMALOUSLY STRONG UPPER RIDGE POSITIONED OVER THE WEST WILL  
LEAD TO A HOT, RECORD-BREAKING, AND POTENTIALLY DANGEROUS HEAT  
WAVE RIGHT THROUGH THIS HOLIDAY WEEKEND INTO NEXT WEEK FOR  
PORTIONS OF THE WESTERN U.S. AND NORTHERN ROCKIES. THE OTHER FOCUS  
FOR SIGNIFICANT WEATHER WILL BE FOUND ACROSS PORTIONS OF TEXAS  
THROUGH THE CENTRAL GULF COAST WHERE INTERACTIONS WITH A STALLING  
FRONTAL BOUNDARY, WEAK UPPER LEVEL DISTURBANCE, AND PLENTIFUL GULF  
MOISTURE COULD BRING MULTIPLE DAYS OF MODERATE TO HEAVY RAINFALL  
AND POTENTIAL FLASH FLOODING. MEANWHILE, SHORTWAVE TROUGHING WILL  
SLIP THROUGH THE NORTHERN TIER OF THE U.S. INTO THE GREAT LAKES  
AND NORTHEAST BRINGING A COUPLE FRONTAL PASSAGES THROUGH THE  
PERIOD. ALONG AND AHEAD OF IT, SHOWERS AND THUNDERSTORMS WILL BE  
POSSIBLE.  
 
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
THE WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY DERIVED FROM A  
COMPOSITE OF REASONABLY WELL CLUSTERED MASS FIELD GUIDANCE FROM  
THE 18Z GFS AND 00Z ECMWF/UKMET/CANADIAN ALONG WITH WPC CONTINUITY  
AND THE 31.01Z NATIONAL BLEND OF MODELS (NBM) DAYS 3-5  
(SATURDAY-MONDAY). THE DETERMINISTIC GUIDANCE AND ENSEMBLE SUPPORT  
SHOWED A SHIFT OF THE HEAVIEST QPF AWAY FROM PORTIONS OF THE LOWER  
MISSISSIPPI VALLEY AND NOW LOOKS TO FOCUS THE GREATEST POTENTIAL  
OF HEAVY RAINFALL THIS WEEKEND OVER CENTRAL GULF COAST TOWARD THE  
TEXAS GULF COAST AND INLAND TOWARD THE HILL COUNTRY. THERE  
CONTINUES TO BE SUPPORT FOR LOW LEVEL SOUTHERLY FLOW AHEAD OF AN  
APPROACHING SHORTWAVE TROUGH OVER THE GREAT LAKES AND A DEVELOPING  
WEAKNESS IN THE RIDGE (POSSIBLY FORMING AN UPPER LOW) OVER THE  
SOUTHERN PLAINS TO HELP DRAW NORTHWARD MORE MOISTURE ACROSS THE  
REST OF THE SOUTHEAST POTENTIALLY INTO PORTIONS OF THE  
MID-ATLANTIC. THIS COULD SUPPORT MORE DIURNALLY DRIVEN CONVECTION  
LATE THIS WEEKEND INTO EARLY NEXT WEEK.  
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
THE STRONG UPPER RIDGE FOR EARLY SEPTEMBER POSITIONED OVER THE  
WESTERN U.S. WILL SUPPORT TEMPERATURES 15-20F ABOVE NORMAL EACH  
DAY WITH THE HOTTEST DAY LIKELY SETTING UP TO BE MONDAY / LABOR  
DAY / WHERE HIGHS IN THE MID TO UPPER 90S WILL ENCOMPASS MUCH OF  
THE WESTERN AREAS, EVEN SPREADING INTO THE NORTHERN PLAINS, AND  
TRIPLE DIGIT READINGS ARE EXPECTED FROM THE DESERT SOUTHWEST  
THROUGH CALIFORNIA CENTRAL VALLEY. WIDESPREAD DAILY HIGH  
TEMPERATURE RECORDS ARE POSSIBLE WITH SOME LOCATIONS POSSIBLY  
REACHING MONTHLY RECORDS. ADDING TO THE HEAT STRESS WILL BE THE  
VERY WARM TO NEAR RECORD OVERNIGHT LOW TEMPERATURES AS WELL. WITH  
LITTLE NIGHTTIME RELIEF AND THE MULTIPLE DAY EVENT EXPECTED, THE  
HEAT WAVE COULD BECOME INCREASINGLY DANGEROUS FOR VULNERABLE  
POPULATIONS THROUGH THE HOLIDAY WEEKEND. WIDESPREAD HIGH TO VERY  
HIGH HEAT RISK LEVELS ARE EXPECTED ALONG AND NEAR THE CENTRAL  
VALLEY AND DESERT REGIONS OF CALIFORNIA THIS WEEKEND INTO EARLY  
NEXT WEEK.  
 
A RESIDUAL FRONTAL BOUNDARY DRAPED ALONG THE GULF COAST  
INTERACTING WITH FAVORABLE GULF MOISTURE TRANSPORT AND A WEAK  
UPPER LEVEL DISTURBANCE WILL HELP FOCUS WIDESPREAD SHOWERS AND  
THUNDERSTORMS THROUGH THE WEEKEND INTO EARLY NEXT WEEK. FOR  
SATURDAY, THE BEST FOCUS FOR HEAVIEST RAINFALL LOOKS TO BE FROM  
THE CENTRAL GULF COAST WESTWARD TO THE TEXAS GULF COAST AND  
POTENTIALLY FURTHER WEST TO THE TX HILL COUNTRY. INTENSE RAIN  
RATES AND PROLONGED WIDESPREAD MODERATE TO HEAVY RAIN COULD TOTAL  
UP TO SEVERAL INCHES AND THIS FALLING OVER AREAS THAT ARE ALREADY  
RUNNING ABOVE NORMAL PRECIPITATION DEPARTURES RECENTLY COULD SPELL  
ADDITIONAL FLASH FLOODING. A SLIGHT RISK IN THE DAY 4 (12Z SAT -  
12Z SUN) EXCESSIVE RAINFALL OUTLOOK REMAINS IN EFFECT FOR THESE  
AREAS. GOING INTO SUNDAY, AN UPPER LEVEL DISTURBANCE DEVELOPING  
OVER THE PLAINS AND THE SURFACE BOUNDARY RETROGRADING WESTWARD  
INTO TEXAS FURTHER WILL BRING ADDITIONAL ROUNDS OF HEAVY RAIN  
POTENTIALLY TO MUCH OF SOUTHERN/SOUTHEAST TEXAS. A SLIGHT RISK IN  
THE DAY 5 (12Z SUN-12Z MON) EXCESSIVE RAINFALL OUTLOOK WAS  
INTRODUCED FOR THESE AREAS. WHILE THE SPECIFICS AND EXACT  
LOCATIONS OF THE HEAVY RAINFALL ARE STILL UNCERTAIN DUE TO THE  
CONVECTIVE/MESOSCALE NATURE OF THE SYSTEM, THE ENVIRONMENTAL  
INGREDIENTS AND LIFT/FOCUS FROM THE SYNOPTIC FEATURES OVER WHAT  
MAY BECOME INCREASINGLY WET ANTECEDENT CONDITIONS COULD LEAD TO  
INSTANCES OF FLASH FLOODING THIS WEEKEND.  
 
TAYLOR  
 
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, EXPERIMENTAL EXCESSIVE RAINFALL  
OUTLOOK, WINTER WEATHER OUTLOOK PROBABILITIES AND HEAT INDICES ARE  
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/#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  
 

 
 

 
 
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