438  
FXUS02 KWBC 040659  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
258 AM EDT SUN SEP 4 2022  
 
VALID 12Z WED SEP 7 2022 - 12Z SUN SEP 11 2022  
 
***RECORD SETTING HEAT WAVE ACROSS THE WESTERN U.S. AND NORTHERN  
PLAINS THROUGH MIDWEEK FOLLOWED BY GRADUAL IMPROVEMENT***  
 
   
..GENERAL SYNOPSIS
 
 
THE MAIN WEATHER HEADLINE GOING INTO THE MIDDLE OF THE WEEK WILL  
CONTINUE TO BE THE ANOMALOUS UPPER LEVEL RIDGE THAT WILL BE  
ANCHORED ACROSS THE WESTERN U.S. THROUGH ABOUT THURSDAY, AND THUS  
A CONTINUANCE OF THE ONGOING SERIOUS AND RECORD SETTING HEAT WAVE  
FROM THE WEST COAST TO THE NORTHERN PLAINS THROUGH THURSDAY,  
FOLLOWED BY A GRADUAL COOLING TREND GOING INTO NEXT WEEKEND.  
ACROSS THE EASTERN U.S., A BROAD UPPER TROUGH AND WEAK CLOSED LOW  
WILL LIKELY BE IN PLACE FOR THE MIDDLE TO END OF THE WEEK ACROSS  
THE DEEP SOUTH AND TENNESSEE RIVER VALLEY, AND MOISTURE FROM A  
TROPICAL DISTURBANCE MAY BEGIN APPROACHING THE SOUTHWESTERN U.S.  
BY THE END OF THE WEEK.  
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
THE 00Z MODEL GUIDANCE SUITE INITIALLY HAS A GOOD OVERALL SYNOPTIC  
SCALE DEPICTION OF THE OVERALL PATTERN ON WEDNESDAY. NOTEWORTHY  
TIMING DIFFERENCES ARE APPARENT BY THURSDAY NIGHT WITH THE GFS  
BECOMING MORE PROGRESSIVE WITH THE TROUGH ACROSS THE NORTHERN  
PLAINS, AND THE CMC IS ON THE SLOWER SIDE OF THE GUIDANCE. THIS  
TROUGH WILL HAVE IMPLICATIONS ON THE BREAK DOWN OF THE HUGE RIDGE  
ACROSS THE WESTERN U.S. LATE THIS WEEK. GOING INTO NEXT WEEKEND,  
THE GFS IS MUCH STRONGER WITH THE TROUGH BUILDING ACROSS THE GREAT  
LAKES, WHEREAS THE ECMWF/CMC ARE MORE INDICATIVE OF A BROAD UPPER  
RIDGE HERE AND THE TROUGH AXIS HOLDING FARTHER WEST. FORECAST  
CONFIDENCE REMAINS BELOW AVERAGE FOR THE FRIDAY THROUGH SUNDAY  
TIME PERIOD WITH POOR MODEL RUN-TO-RUN CONTINUITY OVER THE PAST 24  
HOURS, AND FUTURE FORECASTS ARE SUBJECT TO SIGNIFICANT REVISIONS  
ONCE THE MODELS COME INTO BETTER ALIGNMENT, PARTICULARLY ACROSS  
THE NORTHERN TIER STATES. IN TERMS OF QPF, THE NBM 4.1 ALONG WITH  
SOME OF THE BIAS CORRECTED MODEL WAS USED AS A BASELINE. TAKING  
THESE FACTORS INTO ACCOUNT, THE WPC FRONTS/PRESSURES FORECAST WAS  
PRIMARILY DERIVED FROM A MULTI-MODEL CONSENSUS THROUGH EARLY  
THURSDAY, FOLLOWED BY A GRADUAL INCREASE OF THE ENSEMBLE MEANS  
WHILST STILL KEEPING SOME OF THE ECMWF TO ACCOUNT FOR INCREASING  
UNCERTAINTIES BY THE END OF THE FORECAST PERIOD.  
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
VERY HOT TEMPERATURES BY EARLY SEPTEMBER STANDARDS ARE FORECAST TO  
CONTINUE INTO THE WORKWEEK FROM CALIFORNIA THROUGH THE GREAT BASIN  
INTO CENTRAL/NORTHERN PORTIONS OF THE ROCKIES AND HIGH PLAINS.  
DAYTIME HIGHS AND OVERNIGHT LOWS ON THE ORDER OF 10-25 DEGREES  
ABOVE AVERAGE WILL BE WIDESPREAD THROUGH PROBABLY THURSDAY, AND  
THIS WILL EQUATE TO HIGHS OF 105-115 DEGREES FOR THE LOWER  
ELEVATIONS OF THE DESERT SOUTHWEST AND EVEN INTO CALIFORNIA'S  
CENTRAL VALLEY, WHILE WIDESPREAD 90S AND SOME LOW 100S ARE  
EXPECTED ACROSS THE INTERMOUNTAIN WEST AND EXTENDING NORTHEAST  
ACROSS EASTERN MONTANA AND THE DAKOTAS. SOME ALL-TIME SEPTEMBER  
HIGH TEMPERATURE RECORDS ARE WITHIN THE REALM OF POSSIBILITY, IN  
ADDITION TO NUMEROUS DAILY RECORD HIGHS. THE MAGNITUDE AND  
DURATION OF THE DANGEROUS HEAT WILL BOTH BE CONTRIBUTORS TO  
POTENTIAL SAFETY CONCERNS FOR SENSITIVE GROUPS SUCH AS THE  
ELDERLY, THOSE WORKING OUTSIDE, AND THOSE WITHOUT AIR  
CONDITIONING. THE GOOD NEWS GOING FORWARD IS THAT THE HEAT SHOULD  
ABATE SOME ACROSS THE NORTHWEST BY THURSDAY, FOLLOWED BY GRADUAL  
IMPROVEMENT TO CLOSE OUT THE WEEK FARTHER SOUTH ACROSS THE  
INTERMOUNTAIN WEST. MEANWHILE, SLIGHTLY BELOW NORMAL HIGHS AND  
AROUND NORMAL LOWS ARE EXPECTED FOR PORTIONS OF TEXAS INTO THE  
SOUTHEAST OWING TO MOSTLY CLOUDY SKIES AND MORE WIDESPREAD SHOWER  
AND THUNDERSTORM COVERAGE.  
 
IN TERMS OF RAINFALL POTENTIAL, A MEANDERING BUT WEAK FRONTAL  
BOUNDARY IS LIKELY TO STAY DRAPED ALONG THE GULF COAST INTO  
SOUTHERN TEXAS FOR MUCH OF THE FORECAST PERIOD, WHICH COMBINED  
WITH DEEP GULF MOISTURE AND A BROAD UPPER LOW, IS FORECAST TO  
PRODUCE SCATTERED TO AT TIMES WIDESPREAD SHOWERS AND  
THUNDERSTORMS. THERE HAS BEEN A TREND FOR HIGHER RAINFALL ACROSS  
THE CENTRAL/EASTERN GULF COAST THROUGH THE LATTER PART OF THE WEEK  
AND INTO SATURDAY, WHILE SHOWERS AND THUNDERSTORMS COULD ALSO  
INCREASE IN COVERAGE ACROSS THE SOUTHEAST AND SOUTHERN  
APPALACHIANS. BY THE END OF THE PERIOD, A SURGE OF INCREASED  
MOISTURE MAY ARRIVE IN THE SOUTHWEST IN CONJUNCTION WITH A  
TROPICAL SYSTEM TO THE SOUTH THAT HAS A VERY GOOD CHANCE OF  
DEVELOPING FURTHER, BASED ON RECENT PROJECTIONS FROM THE NATIONAL  
HURRICANE CENTER.  
 
HAMRICK  
 
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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