692  
FXUS02 KWBC 062042  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
439 PM EDT TUE SEP 06 2022  
 
VALID 12Z FRI SEP 09 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...  
 
   
..OVERVIEW
 
 
THE INTENSE WESTERN U.S. UPPER LEVEL RIDGE AND ITS ASSOCIATED  
RECORD SETTING HEAT WAVE SHOULD BE ERODED TO SOME EXTENT BY THE  
START OF THE PERIOD EARLY FRIDAY AS AN UPPER TROUGH REACHES THE  
NORTHERN ROCKIES. WEAKER RIDGING THAT REMAINS OVER PARTS OF THE  
WEST WILL MERGE WITH A PROGRESSIVE NORTHEAST PACIFIC RIDGE TO  
BRING A BRIEF PERIOD OF WARM TO HOT TEMPERATURES INTO THE  
NORTHWEST, FOLLOWED BY A COOLING TREND AS WEAK MEAN TROUGHING  
ALOFT NEARS THE WEST COAST EARLY NEXT WEEK. MOISTURE FROM  
HURRICANE KAY (CURRENTLY FORECAST TO TRACK JUST WEST OF BAJA  
CALIFORNIA) WILL ALSO BEAR WATCHING AS IT WILL LIKELY INCREASE  
RAINFALL OVER PARTS OF SOUTHERN CALIFORNIA AND ARIZONA BY THIS  
WEEKEND. MEANWHILE A BROAD TROUGH/UPPER LOW SHOULD BE IN PLACE  
OVER THE SOUTH THROUGH SUNDAY. THIS FEATURE AND A WAVY SURFACE  
FRONT WILL LIKELY SUPPORT SCATTERED TO NUMEROUS SHOWERS AND STORMS  
FROM THE CENTRAL GULF COAST TO THE SOUTHEAST STATES AND  
APPALACHIANS. GUIDANCE SHOWS AN IMPROVING SIGNAL FOR NORTHERN  
TIER UPPER TROUGH ENERGY TO FORM AN UPPER LOW THAT MAY TRACK OVER  
THE MIDWEST/GREAT LAKES DURING THE FIRST HALF OF NEXT WEEK. THIS  
SYSTEM COULD PRODUCE SOME ENHANCED RAINFALL IN ITS VICINITY AS  
WELL AS SPREAD A BROADER SHIELD OF RAIN OVER THE EAST AS THE  
OVERALL TROUGH INTERACTS WITH THE MOISTURE INITIALLY OVER THE  
SOUTH.  
 
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
FROM THE LARGE SCALE PERSPECTIVE, THE MOST NOTABLE GUIDANCE  
CONSIDERATION IS THE IMPROVED SIGNAL WITH RESPECT TO AN UPPER LOW  
EXPECTED TO FORM OVER THE MIDWEST AROUND SUNDAY-MONDAY AND THEN  
TRACK INTO OR NEAR THE GREAT LAKES BY TUESDAY. UP TO THIS POINT  
THE ECMWF/ECMWF MEAN HAVE BEEN MORE CONSISTENT IN SHOWING THIS  
EVOLUTION, OR AT LEAST A FAIRLY AMPLIFIED UPPER TROUGH. THE  
06Z/12Z GFS RUNS HAVE FALLEN IN LINE WITH THIS SCENARIO, AS HAVE  
THE LAST COUPLE CMC RUNS. THE NEW 12Z UKMET STRAYS A BIT  
SOUTHWEST OF CONSENSUS BY EARLY MONDAY (AS DID THE 00Z GFS). THE  
12Z ECMWF HAS ADJUSTED FARTHER SOUTH WITH ITS UPPER LOW LATE IN  
THE PERIOD, HIGHLIGHTING THE CONTINUED UNCERTAINTY FOR SPECIFICS.  
THE GEFS MEAN MAY STILL BE LAGGING A BIT ON THE DEGREE OF FLOW  
SEPARATION BUT IS CLOSER FOR THE OVERALL UPPER TROUGH. FARTHER  
WEST, SOME SPREAD DEVELOPS REGARDING HEIGHT FALLS MOVING INTO THE  
WEST AHEAD OF A WEAK UPPER LOW EJECTING FROM THE EASTERN PACIFIC  
AS WELL AS WITH POSSIBLE UPSTREAM ENERGY. AN INTERMEDIATE  
SOLUTION BETWEEN THE FASTER 06Z GFS/00Z CMC AND SLOWER 00Z  
ECMWF/GFS AS WELL AS 06Z GEFS/00Z ECMWF MEANS. ALSO NOTE THAT THE  
00Z GFS STRAYED OUT OF PHASE WITH CONSENSUS OVER SOUTHERN CANADA  
LATE IN THE PERIOD. FORECAST CONSIDERATIONS LED TO AN OPERATIONAL  
MODEL COMPOSITE FOR THE FIRST HALF OF THE PERIOD, WITH GREATEST  
WEIGHT ON THE 00Z ECMWF AND 06Z GFS. THEN THE BLEND STARTING TO  
INCORPORATE SOME 06Z GEFS/00Z ECMWF MEAN INPUT ALONG WITH THE  
ECMWF/GFS/CMC, WITH SOMEWHAT MORE ECENS RELATIVE TO THE GEFS GIVEN  
BETTER DEFINITION OF THE FORMER OVER THE EAST.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
THE INTENSE AND LONG DURATION HEAT WAVE THAT IS ENCOMPASSING MUCH  
OF THE WESTERN U.S. AND CENTRAL/NORTHERN PLAINS SHOULD PEAK BEFORE  
THE BEGINNING OF THE FORECAST PERIOD FRIDAY. HOWEVER STILL EXPECT  
ABOVE NORMAL TEMPERATURES ACROSS MUCH OF CALIFORNIA AND THE GREAT  
BASIN ON FRIDAY (WITH SOME PLUS 10-20F ANOMALIES OVER PARTS OF  
CALIFORNIA). WARM TO HOT TEMPERATURES SHOULD SHIFT MORE INTO THE  
PACIFIC NORTHWEST FOR THE WEEKEND FOLLOWED BY GRADUAL MODERATION  
FROM WEST TO EAST. THE NORTHERN-CENTRAL HIGH PLAINS WILL SEE  
HIGHS UP TO 15-20F BELOW NORMAL FRIDAY-SATURDAY, A PRONOUNCED  
CHANGE FROM THE HOT TEMPERATURES EXPECTED DURING THE SHORT RANGE  
TIME FRAME. LESS EXTREME COOL HIGHS WILL SPREAD INTO THE  
CENTRAL/EAST-CENTRAL U.S. BY THE FIRST HALF OF NEXT WEEK UNDER THE  
UPPER TROUGH/LOW FORECAST TO TRAVEL OVER THESE AREAS WHILE CLOUDS  
AND RAINFALL WILL TEND TO PROMOTE BELOW AVERAGE HIGHS OVER THE  
SOUTH/SOUTHEAST.  
 
IN TERMS OF RAINFALL POTENTIAL, A MEANDERING WEAK FRONTAL BOUNDARY  
SHOULD REMAIN ALONG THE GULF COAST AND SOUTHEAST U.S. COAST  
THROUGH THE WEEKEND AND INTERACT WITH DEEP GULF MOISTURE AND A  
BROAD UPPER LOW 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 DEPICTED FROM THE FLORIDA PANHANDLE TO THE  
SOUTHERN APPALACHIANS TO REFLECT THIS POSSIBILITY. 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 ONWARD. MEANWHILE A SURGE OF  
INCREASED MOISTURE WILL LIKELY ARRIVE INTO THE DESERT SOUTHWEST 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 SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA  
ON SATURDAY. THE COVERAGE AND INTENSITY OF RAINFALL FARTHER NORTH  
OVER THE WESTERN U.S. IS STILL A QUESTION MARK, AS MOISTURE WILL  
BE ANOMALOUSLY HIGH BUT GUIDANCE INSTABILITY IS NOT PARTICULARLY  
IMPRESSIVE AND UPPER TROUGHING THAT EVENTUALLY DEVELOPS OFF THE  
WEST COAST IS FAIRLY MODEST.  
 
RAUSCH/HAMRICK  
 
HAZARDS:  
- HEAVY RAIN ACROSS PORTIONS OF THE SOUTHEASTERN U.S. INTO THE  
TENNESSEE VALLEY, AS WELL AS PORTIONS OF SOUTHERN CALIFORNIA,  
FRI-SAT, SEP 9-SEP 10.  
- HEAVY RAIN ACROSS PORTIONS OF THE SIERRA NEVADA, SAT-SUN, SEP  
10-SEP 11.  
- HEAVY RAIN ACROSS PORTIONS OF THE UPPER MIDWEST TO THE GREAT  
LAKES, CENTRAL TO SOUTHERN APPALACHIANS, THE INTERIOR  
MID-ATLANTIC, INTERIOR SOUTHEAST, AS WELL AS ACROSS THE EASTERN  
GULF COAST/NORTHERN FLORIDA, SUN-MON, SEP 11-SEP 12.  
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE LOWER  
MISSISSIPPI VALLEY.  
- EXCESSIVE HEAT ACROSS PORTIONS OF THE INTERIOR VALLEYS OF  
CALIFORNIA, FRI, SEP 9.  
 
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  
 

 
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page