209  
FXUS02 KWBC 311903  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
302 PM 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 AMONG A STALLING  
FRONTAL BOUNDARY, A 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 AND SEASONABLE TEMPERATURES. ALONG AND AHEAD OF  
EACH FRONT, SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE.  
 
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
UPPER PATTERN WILL FEATURE A STRONG UPPER HIGH OVER THE GREAT  
BASIN/SOUTHWEST TO START THE PERIOD (SAT) WITH WEAKER RIDGING OVER  
THE WESTERN ATLANTIC. THIS WILL FAVOR POSITIVELY-TILTED TROUGHING  
FROM TEXAS TO THE GREAT LAKES. THROUGH THE WEEKEND INTO NEXT WEEK,  
THE UPPER HIGH IS FORECAST TO FLATTEN A BIT AS A SHORTWAVE OR  
CLOSED LOW PUSHES INTO THE PAC NW AND WESTERN CANADA, WITH SOME  
DISAGREEMENT ON TIMING. THE CLUSTER ANALYSIS SHOWS A RELATIVELY  
EVENLY-DIVIDED SPLIT AMONG THE GLOBAL ENSEMBLES, SUGGESTING A  
GENERAL BLEND/CONSENSUS APPROACH WAS THE BEST APPROACH TO THE  
FORECAST TODAY. THE 13Z NBM WAS UTILIZED FOR THE SENSIBLE WEATHER  
GRIDS AND A BLEND OF THE GFS/GEFS AND ECMWF/EPS WAS USED FOR THE  
PRESSURE FIELDS/WINDS, MAINTAINING GOOD CONTINUITY FROM OVERNIGHT.  
   
..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 PER THE GUIDANCE. MANY AREAS ARE ALREADY  
RUNNING ABOVE NORMAL PRECIPITATION DEPARTURES RECENTLY WHICH COULD  
SPELL ADDITIONAL FLASH FLOODING. A SLIGHT RISK IN THE EXPERIMENTAL  
DAY 4 (12Z SAT - 12Z SUN) EXCESSIVE RAINFALL OUTLOOK REMAINS IN  
EFFECT FOR THESE AREAS. GOING INTO SUNDAY, TROUGHING 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  
EXPERIMENTAL DAY 5 (12Z SUN-12Z MON) EXCESSIVE RAINFALL OUTLOOK  
WAS MAINTAINED FOR THESE AREAS FROM OVERNIGHT. 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.  
 
FRACASSO/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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