871  
FXUS02 KWBC 010655  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
254 AM EDT THU SEP 01 2022  
 
VALID 12Z SUN SEP 04 2022 - 12Z THU SEP 08 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
 
 
THE ANOMALOUSLY STRONG UPPER RIDGE OVER THE WEST WILL PERSIST  
THROUGH THE MIDDLE OF NEXT WEEK, BRINGING HOT, RECORD-BREAKING,  
AND POTENTIALLY DANGEROUS HEAT TO PORTIONS OF THE WESTERN U.S.  
INTO THE 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. ACROSS THE NORTHERN TIER OF THE U.S. INTO THE NORTHEAST,  
A FEW FRONTAL PASSAGES ARE EXPECTED BRINGING CHANCES OF SHOWERS  
AND THUNDERSTORMS AHEAD OF IT. BY THE END OF THE FORECAST PERIOD,  
THE HEAT OVER THE WEST WILL BEGIN TO SUBSIDE AND SHIFT EASTWARD AS  
A STRONGER SHORTWAVE TROUGH MOVES INTO THE PACIFIC NORTHWEST.  
 
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
FAIRLY STRONG AGREEMENT AND PREDICTABILITY WITH THE LARGE SCALE  
PATTERN OVER THE CONUS THROUGH ABOUT DAY 5. THE WESTERN U.S. UPPER  
RIDGE WILL REMAIN CENTERED OVER THE GREAT BASIN AND A SLOW MOVING  
POSITIVELY TILTED TROUGH OVER THE CENTRAL TO EASTERN U.S.. BY DAY  
5, THE WESTERN RIDGE FLATTENS A BIT AS DEEP TROUGHING OVER THE  
EASTERN PACIFIC BEGINS TO MOVE EASTWARD WITH THE APPROACH A  
STRONGER SHORTWAVE TROUGH DIGGING THROUGH. THAT ENERGY IS LIKELY  
TO REACH THE PACIFIC NORTHWEST DAY 6 INTO DAY 7, THOUGH THERE  
REMAINS SOME TIMING DIFFERENCES AMONG THE VARIOUS DETERMINISTIC  
GUIDANCE. 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 01.01Z 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 WPC CONTINUITY.  
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
AN EARLY SEPTEMBER HEATWAVE ACROSS THE WESTERN U.S. IS EXPECTED TO  
PRODUCE DAILY HIGH TEMPERATURE ANOMALIES OF 10-20F EACH DAY WITH  
THE HOTTEST DAY ON TRACK TO BE MONDAY /LABOR DAY/ FOR PORTIONS OF  
CALIFORNIA WHILE THE HEAT PEAKS TUESDAY AND WEDNESDAY FOR THE  
NORTHERN ROCKIES AHEAD OF AN APPROACHING FRONTAL PASSAGE. READINGS  
WELL INTO THE 90S WITH TRIPLE DIGIT READINGS EXPECTED FOR THE  
DESERT SOUTHWEST INTO THE 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  
SUNDAY, THE FOCUS FOR THE HEAVIEST RAIN POTENTIAL REMAINS ACROSS  
PORTIONS OF SOUTHERN TO SOUTHEAST TEXAS WHERE THE COMBINATION OF  
INTENSE RAIN RATES AND PROLONGED WIDESPREAD MODERATE TO HEAVY RAIN  
COULD TOTAL A FEW INCHES PER THE LATEST FORECAST 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 SUN - 12Z MON) EXCESSIVE  
RAINFALL OUTLOOK REMAINS IN EFFECT FOR THESE AREAS. BY SUNDAY, THE  
BOUNDARY BECOMES MORE DIFFUSE AND THE SIGNAL FOR HEAVY RAIN ISN'T  
AS STRONG THOUGH SOMETHING TO MONITOR OVER THE COMING DAYS ACROSS  
SOUTHERN TEXAS. GUIDANCE ALSO POINTS TO FAVORABLE MOISTURE  
TRANSPORT AND LIFT OVER THE SOUTHERN APPALACHIANS WHERE RAIN  
TOTALS COULD REACH A FEW INCHES OVER THE NEXT WEEK AND THIS AREA  
WILL NEED TO BE MONITORED FOR POTENTIAL HEAVY RAIN AND FLASH  
FLOODING OVER THE COMING DAYS TOO.  
 
TAYLOR/FRACASSO  
 
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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