003  
FXUS02 KWBC 070659  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
258 AM EDT WED SEP 7 2022  
 
VALID 12Z SAT SEP 10 2022 - 12Z WED SEP 14 2022  
 
***HEAVY RAIN AND POTENTIAL FLOODING A CONCERN ACROSS PARTS OF THE  
SOUTHEAST U.S. AND DESERT SOUTHWEST***  
 
   
..GENERAL OVERVIEW
 
 
A PATTERN CHANGE WILL BE UNDERWAY ACROSS MUCH OF THE WESTERN U.S.  
AND THE NORTHERN PLAINS/MIDWEST AS A STRONG COLD FRONT HERALDS A  
CHANGE TO MUCH COOLER TEMPERATURES FOR THE WEEKEND, COMPARED TO  
THE INTENSE LATE SEASON HEAT WAVE THAT IS CURRENTLY ONGOING. THE  
UPPER TROUGH THAT IS ACCOMPANYING THIS FRONT IS EXPECTED TO EVOLVE  
INTO A CLOSED UPPER LOW ACROSS THE OHIO VALLEY AND GREAT LAKES  
REGION GOING INTO EARLY NEXT WEEK, WITH A RIDGE AXIS NEAR THE EAST  
COAST BLOCKING ITS EASTWARD PROGRESSION. MOISTURE ASSOCIATED WITH  
WHAT WILL EVENTUALLY BE THE REMNANTS OF HURRICANE KAY IS EXPECTED  
TO ADVECT INLAND ACROSS MUCH OF SOUTHERN CALIFORNIA, NEVADA, AND  
WESTERN ARIZONA, WHICH WILL BE A WELCOME CHANGE FROM THE ONGOING  
DROUGHT AND MISERABLY HOT CONDITIONS. THERE WILL LIKELY BE  
ANOTHER TROUGH APPROACHING THE PACIFIC NORTHWEST LATE 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 THROUGH EARLY SUNDAY WITH  
THE TYPICAL MESOSCALE MODEL DIFFERENCES. AS THE UPPER LOW BUILDS  
IN ACROSS THE MIDWEST BY MONDAY, THE GFS IS NORTHEAST OF THE WELL  
CLUSTERED ECMWF/CMC SOLUTIONS, AND THIS CONTINUES GOING INTO  
WEDNESDAY AS WELL. THE CMC DEVELOPS A STRONGER TROUGH IN THE  
NORTHERN STREAM ACROSS CANADA BY WEDNESDAY, BUT IS OTHERWISE  
FAIRLY CLOSE TO THE MODEL CONSENSUS WITH THE TROUGH NEAR THE WEST  
COAST REGION. IN TERMS OF QPF, THE NBM ALONG WITH A LITTLE OF THE  
OPERATIONAL 12Z ECMWF WAS USED AS A BASELINE. THE WPC  
FRONTS/PRESSURES FORECAST UTILIZED A MULTI-MODEL DETERMINISTIC  
BLEND THROUGH MONDAY, GRADUALLY INCREASING USE OF THE ECMWF AND  
GEFS MEANS TO ABOUT HALF BY THE END OF THE PERIOD AS INDIVIDUAL  
MODEL DIFFERENCES INCREASE, WITH LESS WEIGHTING TOWARDS THE GFS  
EARLY NEXT WEEK.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
THE FIRST STRONG COLD FRONT OF SEPTEMBER IS FORECAST TO BRING  
QUITE A CHANGE TO THE ROCKIES EASTWARD TO THE WESTERN HIGH PLAINS  
AND EXTENDING INTO MINNESOTA FOR THE UPCOMING WEEKEND. HIGHS ARE  
EXPECTED TO BE ONLY IN THE UPPER 50S TO UPPER 60S FOR MANY OF  
THESE AREAS ON SATURDAY, WHICH IS ROUGHLY 10-20 DEGREES BELOW  
NORMAL FOR THIS TIME OF YEAR FOR EASTERN COLORADO/WYOMING AND  
WESTERN NEBRASKA. THIS WILL BE A WELCOME RELIEF COMPARED TO THE  
HEAT WAVE EARLIER IN THE WEEK. SIGNIFICANT ABATEMENT OF THE HEAT  
IS ALSO EXPECTED ACROSS CALIFORNIA AND DESERT SOUTHWEST, WITH MUCH  
OF THIS COOL DOWN ATTRIBUTABLE TO CLOUDS AND RAINFALL ASSOCIATED  
WITH A WEAKENING TROPICAL STORM KAY BY THAT TIME. BY SUNDAY INTO  
MONDAY, TEMPERATURES WARM UP AGAIN TO SLIGHTLY ABOVE AVERAGE  
LEVELS ACROSS THE NORTHWESTERN U.S., BUT NOT TO THE SAME MAGNITUDE  
AS THIS PAST WEEK. ACROSS THE EASTERN U.S., READINGS SHOULD  
GENERALLY BE WITHIN 5 DEGREES OF CLIMATOLOGICAL AVERAGES FOR  
HIGHS, WHILE OVERNIGHT LOWS NEAR THE EAST COAST SHOULD BE ABOUT  
5-10 DEGREES ABOVE NORMAL MOST NIGHTS.  
 
IN TERMS OF RAINFALL POTENTIAL, A WEAKENING FRONT NEAR GULF COAST  
AND SOUTHEAST U.S. COAST, IN COMBINATION WITH A WEAK UPPER  
TROUGH/LOW THROUGH THE WEEKEND, WILL INTERACT WITH DEEP GULF  
MOISTURE TO PRODUCE NUMEROUS SHOWERS AND THUNDERSTORMS FOR THE  
SOUTHEAST U.S. ON SATURDAY. THERE IS ALSO THE POTENTIAL FOR  
INSTANCES OF FLOODING WHERE MULTIPLE ROUNDS OF CONVECTION DEVELOP,  
AND A SLIGHT RISK OF EXCESSIVE RAINFALL IS DEPICTED ACROSS THE  
SOUTHERN APPALACHIANS TO REFLECT THIS POSSIBILITY. A SURGE OF  
INCREASED MOISTURE IS EXPECTED TO BE IN PLACE ACROSS THE DESERT  
SOUTHWEST AND CALIFORNIA BY THE WEEKEND IN CONJUNCTION WITH THE  
EVENTUAL REMNANTS OF WHAT IS NOW HURRICANE KAY, BASED ON RECENT  
PROJECTIONS FROM THE NATIONAL HURRICANE CENTER. A SLIGHT RISK FOR  
EXCESSIVE RAINFALL IS ALSO IN AFFECT FOR PORTIONS OF  
CENTRAL/SOUTHERN CALIFORNIA ON SATURDAY. THE COVERAGE AND  
INTENSITY OF RAINFALL FARTHER NORTH OVER THE WESTERN U.S. IS STILL  
A BIT UNCERTAIN, AS MOISTURE WILL BE ANOMALOUSLY HIGH BUT  
INSTABILITY IS MORE LIMITED AND UPPER TROUGHING THAT EVENTUALLY  
DEVELOPS OFF THE WEST COAST IS FAIRLY MODEST. ELSEWHERE, A WAVY  
FRONT PUSHING INTO THE CENTRAL PLAINS/UPPER GREAT LAKES LATE THIS  
WEEK INTO THE WEEKEND MAY PRODUCE ONE OR MORE BANDS OF LOCALLY  
MODERATE TO HEAVY PRECIPITATION. SPECIFICS WILL TAKE SOME  
ADDITIONAL TIME TO RESOLVE. EXPECTED CLOSING OF AN UPPER LOW OVER  
THE MIDWEST/GREAT LAKES COULD MAINTAIN AN AXIS OF ENHANCED  
RAINFALL IN ITS VICINITY. THE OVERALL UPPER TROUGH ANCHORED BY  
THIS UPPER LOW AND THE LEADING SURFACE SYSTEM MAY INTERACT WITH  
THE MOISTURE INITIALLY OVER THE SOUTH TO SPREAD A BROADER SHIELD  
OF RAINFALL OVER THE EASTERN U.S. FROM SUNDAY INTO EARLY NEXT  
WEEK.  
 
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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