576  
FXUS02 KWBC 050657  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
256 AM EDT MON SEP 5 2022  
 
VALID 12Z THU SEP 8 2022 - 12Z MON SEP 12 2022  
 
***RECORD SETTING HEAT WAVE ACROSS THE WESTERN U.S. AND NORTHERN  
PLAINS THROUGH THURSDAY FOLLOWED BY GRADUAL IMPROVEMENT***  
 
   
..GENERAL SYNOPSIS
 
 
THE INTENSE UPPER LEVEL RIDGE AND THE RECORD SETTING HEAT WAVE  
ASSOCIATED WITH IT IS FORECAST TO SLOWLY ERODE AND WEAKEN AS  
SHORTWAVE ENERGY FROM THE NORTH IMPINGES UPON IT, THUS HERALDING A  
BIT OF A PATTERN CHANGE GOING INTO THE WEEKEND. A BROAD UPPER  
LOW/TROUGH IS FORECAST TO BE IN PLACE ACROSS THE DEEP SOUTH  
THROUGH SUNDAY, AND THIS IN COMBINATION WITH A WEAK FRONTAL  
BOUNDARY, WILL TEND TO RESULT IN SCATTERED TO NUMEROUS SHOWERS AND  
STORMS FROM TEXAS TO THE SOUTHEAST STATES. TROPICAL STORM KAY  
ALSO BEARS WATCHING AS THE EVENTUAL REMNANTS OF THIS STORM COULD  
RESULT IN AN INCREASE IN RAINFALL ACROSS PORTIONS OF THE SOUTHWEST  
U.S. LATER IN THE FORECAST PERIOD.  
 
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
THE 00Z MODEL GUIDANCE SUITE INITIALLY HAS A GOOD OVERALL SYNOPTIC  
SCALE DEPICTION OF THE OVERALL PATTERN ON THURSDAY AND EVEN  
CONTINUING INTO FRIDAY. THE DETERMINISTIC MODEL GUIDANCE HAS COME  
INTO BETTER FOCUS ON THE SHORTWAVE PERTURBATIONS ACROSS THE  
NORTHERN TIER STATES COMPARED TO THE PAST FEW DAYS. HOWEVER, THE  
GFS REMAINS MORE PROGRESSIVE WITH THE TROUGH ACROSS THE  
NORTHEASTERN U.S., WHEREAS THE ECMWF/CMC ARE IN GOOD AGREEMENT ON  
A CUT-OFF LOW DEVELOPING OVER THE GREAT LAKES BY SUNDAY/MONDAY.  
THE CMC BECOMES STRONGER WITH A SHORTWAVE TROUGH APPROACHING THE  
PACIFIC NORTHWEST BY NEXT MONDAY AND HAS LIMITED ENSEMBLE SUPPORT.  
IN TERMS OF QPF, THE NBM 4.1 ALONG WITH SOME OF THE BIAS  
CORRECTED MODEL WAS USED AS A BASELINE.  
 
THE WPC FRONTS/PRESSURES FORECAST UTILIZED A MULTI-MODEL  
DETERMINISTIC BLEND FOR THE END OF THE WEEK, GRADUALLY INCLUDING  
AND INCREASING THE PROPORTION OF THE ECMWF AND GEFS MEANS TO ABOUT  
HALF BY THE END OF THE PERIOD AS INDIVIDUAL MODEL DIFFERENCES  
INCREASED. THE FORECAST WAS FAIRLY CONSISTENT WITH CONTINUITY,  
WITH ONE CHANGE BEING AN INCREASE IN RAINFALL TOTALS ACROSS THE  
SOUTHEAST U.S., WHERE A SLIGHT RISK OF EXCESSIVE RAINFALL WAS  
INTRODUCED FOR THE DAY 5 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 105-110 DEGREES FOR THE LOWER  
ELEVATIONS OF THE DESERT SOUTHWEST AND EVEN INTO CALIFORNIA'S  
CENTRAL VALLEY, WHILE WIDESPREAD 90S ARE EXPECTED ACROSS THE  
INTERMOUNTAIN WEST AND EXTENDING NORTHEAST ACROSS EASTERN MONTANA  
AND THE DAKOTAS. 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 AND ESPECIALLY ACROSS THE  
NORTHERN PLAINS, WHERE THE CHANGE TO COOLER WEATHER WILL LIKELY BE  
MORE NOTICEABLE. 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. BY THE END OF THE PERIOD, A SURGE OF INCREASED  
MOISTURE WILL LIKELY ARRIVE FOR THE DESERT SOUTHWEST IN  
CONJUNCTION WITH THE EVENTUAL REMNANTS OF TROPICAL STORM KAY,  
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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