723  
FXUS02 KWBC 072039  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
438 PM EDT WED SEP 07 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...  
 
   
..OVERVIEW
 
 
THE WEST WILL SEE STEADY PROGRESS TOWARD A PATTERN CHANGE BRINGING  
COOLER CONDITIONS COMPARED TO THE INTENSE HEAT WAVE CURRENTLY IN  
PROGRESS OVER THE REGION. MOISTURE ASSOCIATED WITH WHAT WILL  
EVENTUALLY BE THE REMNANTS OF HURRICANE KAY WILL PUSH INLAND  
ACROSS MUCH OF SOUTHERN CALIFORNIA, NEVADA, AND WESTERN ARIZONA,  
LIKELY PRODUCING AN AREA OF ENHANCED RAINFALL INTO THE WEEKEND.  
SOME OF THIS MOISTURE IN LESS PRONOUNCED FORM SHOULD REACH THE  
GREAT BASIN AND ROCKIES AS A MEAN TROUGH AXIS SETS UP NEAR THE  
WEST COAST. MEANWHILE THE GUIDANCE AGREES IN PRINCIPLE THAT A  
NORTHERN ROCKIES/PLAINS UPPER TROUGH SHOULD CLOSE OFF A LOW THAT  
TRACKS OVER THE MIDWEST AND OHIO VALLEY/GREAT LAKES REGION. THIS  
EVOLUTION ALONG WITH THE INITIAL WAVY SURFACE FRONT THAT  
EVENTUALLY BECOMES AN OCCLUDED SYSTEM WILL LIKELY PRODUCE AN AREA  
OF ENHANCED RAINFALL, WHILE A BROADER SHIELD OF RAIN SHOULD SPREAD  
OVER THE EASTERN U.S. AS THIS SYSTEM INTERACTS WITH AN AREA OF  
MOISTURE ALREADY PRODUCING RAIN AND THUNDERSTORMS OVER THE  
SOUTHEAST AND VICINITY. BETWEEN THE EVENTUAL TROUGHS OVER THE  
WEST COAST AND EAST-CENTRAL U.S., UPPER RIDGING SHOULD PROGRESS  
THROUGH THE WEST AND INTO THE PLAINS.  
 
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
TRENDS OVER THE PAST DAY HAVE GENERALLY BEEN GRAVITATING CLOSER TO  
THE 00Z ECMWF/ECMWF MEAN FOR THE PATH OF THE EAST-CENTRAL U.S.  
UPPER LOW, LEANING TO THE SOUTHWESTERN HALF OF THE PRIOR ENVELOPE.  
THE 06Z GFS/GEFS MEAN HAVE ADJUSTED SOMEWHAT SOUTHWEST OF THEIR  
00Z RUNS BUT ARE STILL NORTHEAST OF THE ECMWF WHILE THE 12Z  
GFS/GEFS HAVE NUDGED A LITTLE FARTHER SOUTH. ON THE OTHER HAND,  
THE 00Z CMC WAS A SOUTHWEST EXTREME BUT THE NEW 12Z RUN ADJUSTED  
TO THE 00Z ECMWF AND THE 12Z UKMET HAS WOBBLED A LITTLE NORTH WITH  
ITS UPPER LOW. THUS A 06Z GFS/00Z ECMWF COMPROMISE TILTED A BIT  
MORE TO THE ECMWF PROVIDED A REASONABLE DEPICTION OF THIS FEATURE.  
THE DEVELOPING MEAN TROUGH ALOFT NEAR THE WEST COAST WILL CONSIST  
OF AN EJECTING EAST PACIFIC UPPER LOW AND THEN UPSTREAM ENERGY  
THAT FEEDS INTO THE OVERALL TROUGH. THERE IS TYPICAL SPREAD WITH  
DETAILS FOR HOW HEIGHT FALLS PUSH INTO THE WEST EARLY-MID WEEK,  
WITH A MODEL/ENSEMBLE MEAN BLEND PROVIDING GOOD CONTINUITY.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
THE FIRST STRONG COLD FRONT OF SEPTEMBER WILL BRING QUITE A CHANGE  
TO THE ROCKIES AND WESTERN HIGH PLAINS INTO THE UPPER MIDWEST FOR  
THE UPCOMING WEEKEND. HIGHS SHOULD BE ONLY IN THE UPPER 50S TO  
UPPER 60S FOR MANY OF THESE AREAS ON SATURDAY, WHICH IS 10-20  
DEGREES OR SO 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. MEANWHILE  
CLOUDS AND RAINFALL FROM KAY WILL BRING COOLER CONDITIONS OVER THE  
SOUTHWEST U.S. THE PACIFIC NORTHWEST WILL SEE ABOVE NORMAL  
TEMPERATURES ON SATURDAY (PLUS 10-20F ANOMALIES) WITH THIS WARMTH  
PROGRESSING EASTWARD THROUGH THE NORTHERN ROCKIES/HIGH PLAINS  
SUNDAY-MONDAY, BUT READINGS WILL NOT BE AS EXTREME AS THIS PAST  
WEEK. THE COOL AIR OVER THE CENTRAL U.S. THIS WEEKEND WILL MODIFY  
AS IT CONTINUES EASTWARD UNDER THE FORECAST UPPER TROUGH/LOW,  
BRINGING HIGHS A FEW DEGREES BELOW NORMAL EARLY-MID WEEK.  
CLOUDS/MOISTURE SHOULD KEEP EASTERN U.S. MORNING LOWS 5-10 DEGREES  
OR SO ABOVE NORMAL.  
 
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. EXPECT A SURGE  
OF INCREASED MOISTURE 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. CURRENTLY EXPECT SOME RAINFALL TO EXTEND INTO THE GREAT  
BASIN AND NORTH-CENTRAL/CENTRAL ROCKIES BY EARLY-MID WEEK.  
FARTHER EAST, A WAVY FRONT PUSHING INTO THE SOUTH-CENTRAL  
PLAINS/UPPER GREAT LAKES AS OF EARLY SATURDAY 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/OHIO VALLEY COULD MAINTAIN  
AN AXIS OF ENHANCED RAINFALL IN ITS VICINITY. THE OVERALL UPPER  
TROUGH ANCHORED BY THIS CLOSED 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  
THROUGH THE FIRST HALF OF NEXT WEEK. IT IS LIKELY THERE WILL BE  
SOME EMBEDDED BANDS OF HEAVIER RAINFALL BUT IT MAY TAKE INTO THE  
SHORT RANGE TIME FRAME BEFORE THE DETAILS COME INTO CLEARER FOCUS.  
 
RAUSCH/HAMRICK  
 
HAZARDS:  
- HEAVY RAIN ACROSS PORTIONS OF THE SOUTHERN CALIFORNIA INTO THE  
SIERRA NEVADA, THE UPPER MIDWEST, THE UPPER TENNESSEE VALLEY, AS  
WELL AS THE SOUTHEAST INCLUDING NORTHERN FLORIDA AND INTO SOUTHERN  
APPALACHIANS, SAT-SUN, SEP 10-SEP 11.  
- HEAVY RAIN ACROSS PORTIONS OF THE SOUTHERN MID-ATLANTIC COAST,  
AND UPSTATE NEW YORK, MON-TUE, SEP 12-SEP 13.  
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE LOWER  
MISSISSIPPI VALLEY.  
 
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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