369  
FXUS02 KWBC 060639  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
239 AM EDT TUE SEP 6 2022  
 
VALID 12Z FRI SEP 9 2022 - 12Z TUE SEP 13 2022  
 
***HEAT WAVE ABATES TO CLOSE OUT THE WEEK ACROSS THE WESTERN  
U.S.***  
 
***HEAVY RAIN AND POTENTIAL FLOODING A CONCERN ACROSS PARTS OF THE  
SOUTHEAST U.S. AND DESERT SOUTHWEST***  
 
   
..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 AND UPPER LEVEL TROUGHING FROM THE NORTH IMPINGES  
UPON IT, THUS HERALDING A WELCOME CHANGE COMPARED TO THE EXTREME  
HEAT DURING THE EARLY TO MIDDLE PART OF THE WEEK. 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 THE CENTRAL GULF COAST TO THE SOUTHEAST STATES AND  
APPALACHIANS. THE EVENTUAL TRACK OF HURRICANE KAY AS IT WEAKENS  
ALSO BEARS WATCHING AS THE EVENTUAL REMNANTS OF THIS STORM WILL  
LIKELY RESULT IN AN INCREASE IN RAINFALL ACROSS SOUTHERN  
CALIFORNIA AND ARIZONA BY THIS WEEKEND.  
 
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
THE 00Z MODEL GUIDANCE SUITE INITIALLY HAS A GOOD OVERALL SYNOPTIC  
SCALE DEPICTION OF THE OVERALL PATTERN THROUGH EARLY SUNDAY WITH  
THE TYPICAL MESOSCALE MODEL DIFFERENCES. BY EARLY NEXT WEEK,  
THERE HAS BEEN A STRONGER TREND FOR A CLOSED LOW TO DEVELOP OVER  
THE MIDWEST STATES, WITH THE GFS FARTHEST SOUTH WITH THE LOW.  
MODELS HAVE ALSO COME INTO BETTER AGREEMENT ON THE NEXT  
TROUGH/SURFACE FRONTS APPROACHING THE PACIFIC COAST LATER IN THE  
FORECAST PERIOD. 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 FRIDAY AND SATURDAY, GRADUALLY INCREASING USE OF THE  
ECMWF AND GEFS MEANS TO ABOUT HALF BY THE END OF THE PERIOD AS  
INDIVIDUAL MODEL DIFFERENCES INCREASE.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
THE INTENSE AND LONG DURATION HEAT WAVE THAT IS ENCOMPASSING MUCH  
OF THE WESTERN U.S. AND CENTRAL/NORTHERN PLAINS IS FORECAST TO  
PEAK BEFORE THE BEGINNING OF THE FORECAST PERIOD FRIDAY. HAVING  
SAID THAT, READINGS ARE STILL EXPECTED TO BE ABOVE NORMAL ACROSS  
MUCH OF CALIFORNIA AND THE INTERMOUNTAIN WEST ON FRIDAY, WHILE AN  
EVEN MORE NOTICEABLE CHANGE IN TEMPERATURES ARE EXPECTED TO ARRIVE  
FOR THE NORTHERN ROCKIES AND NORTHERN PLAINS AS A STRONG COLD  
FRONT BRINGS A WELCOME CHANGE TO COOLER CONDITIONS AND EVEN SOME  
BELOW AVERAGE READINGS. MEANWHILE, SLIGHTLY BELOW NORMAL HIGHS  
AND AROUND NORMAL LOWS ARE EXPECTED FOR THE SOUTH-CENTRAL U.S.  
INTO THE SOUTHEAST OWING TO MOSTLY CLOUDY SKIES AND MORE  
WIDESPREAD SHOWER AND THUNDERSTORM COVERAGE. SLIGHTLY BELOW  
AVERAGE READINGS ARE ALSO BECOMING MORE LIKELY ACROSS MUCH OF THE  
CENTRAL PLAINS AND MIDWEST GOING INTO THE WEEKEND AND MONDAY.  
 
IN TERMS OF RAINFALL POTENTIAL, A MEANDERING BUT WEAK FRONTAL  
BOUNDARY IS LIKELY TO STAY DRAPED ALONG THE GULF COAST AND  
SOUTHEAST U.S. COAST THROUGH THE WEEKEND, WHICH COMBINED WITH DEEP  
GULF MOISTURE AND A BROAD UPPER LOW, IS FORECAST TO PRODUCE  
NUMEROUS SHOWERS AND THUNDERSTORMS. THERE IS ALSO THE POTENTIAL  
FOR INSTANCES OF FLOODING WHERE MULTIPLE ROUNDS OF CONVECTION  
DEVELOP, AND A SLIGHT RISK OF EXCESSIVE RAINFALL IS IN EFFECT FROM  
THE FLORIDA PANHANDLE TO THE SOUTHERN APPALACHIANS TO ACCOUNT FOR  
THIS. BY THE WEEKEND, A SURGE OF INCREASED MOISTURE WILL LIKELY  
ARRIVE FOR THE DESERT SOUTHWEST IN CONJUNCTION WITH THE EVENTUAL  
REMNANTS OF WHAT IS NOW HURRICANE KAY, BASED ON RECENT PROJECTIONS  
FROM THE NATIONAL HURRICANE CENTER, AND A SLIGHT RISK FOR  
EXCESSIVE RAINFALL IS ALSO IN AFFECT FOR PORTIONS OF SOUTHEAST  
CALIFORNIA AND SOUTHWEST ARIZONA ON SATURDAY.  
 
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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