772  
FXUS02 KWBC 052018  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
418 PM EDT MON SEP 05 2022  
 
VALID 12Z THU SEP 08 2022 - 12Z MON SEP 12 2022  
 
...RECORD SETTING HEAT WAVE ACROSS PARTS OF 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 BY  
THURSDAY AS SHORTWAVE ENERGY MOVES INTO THE NORTHWEST, WITH  
SOMEWHAT OF A PATTERN CHANGE GOING INTO THE WEEKEND. A  
BROAD/CUT-OFF UPPER LOW/TROUGH IS FORECAST TO BE IN PLACE ACROSS  
THE DEEP SOUTH INTO THIS WEEKEND, AND THIS IN COMBINATION WITH A  
WEAK FRONTAL BOUNDARY, WILL TEND TO RESULT IN ENHANCED TO  
POTENTIALLY HEAVY/EXCESSIVE RAINFALL ALONG THE GULF COAST AND INTO  
THE SOUTHEAST. TROPICAL STORM KAY ALSO BEARS WATCHING AS THE TRACK  
OF THIS SYSTEM TO NEAR/OFF THE COAST OF CALIFORNIA COULD RESULT IN  
AN INCREASE IN RAINFALL ACROSS PORTIONS OF THE SOUTHWEST U.S.  
LATER IN THE FORECAST PERIOD.  
 
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
THE LATEST MODEL GUIDANCE SUITE CONTINUES TO SHOW GOOD SYNOPTIC  
SCALE AGREEMENT THROUGH DAY 5 ON THE OVERALL PATTERN FEATURING A  
SHORTWAVE TROUGH MOVING THROUGH THROUGH THE NORTHWEST INTO THE  
NORTHERN U.S. AND A CUT OFF BROAD UPPER LOW NEARLY STAGNANT OVER  
THE CENTRAL GULF COAST. A GENERAL MODEL COMPROMISE SEEMED TO SERVE  
AS A GOOD STARTING POINT ACROSS THE BOARD FOR DAYS 3 TO 5. THIS  
WEEKEND, AND ESPECIALLY BEYOND, SOME LARGER SCALE DIFFERENCES  
BEGIN TO CREEP UP, INCLUDING SOME QUESTION ON TIMING OF THE  
SHORTWAVE ACROSS THE UPPER MIDWEST AND DETAILS SURROUNDING ITS THE  
EVOLUTION OF A CUT-OFF LOW TAKING SHAPE OVER THE MIDWEST/OHIO  
VALLEY EARLY NEXT WEEK. MOST OF THE DETERMINISTIC MODEL SOLUTIONS  
HAVE BEEN CONSISTENT IN SHOWING THIS EVOLUTION, HOWEVER THE  
ENSEMBLE MEANS ONLY SHOW A WEAKER SHORTWAVE, WHICH SUGGESTS QUITE  
A BIT OF UNCERTAINTY STILL SURROUNDS THIS FEATURE. OUT WEST, THE  
NEXT TROUGH APPROACHES BY SUNDAY WITH SOME GREATER TIMING AND  
STRENGTH DIFFERENCES. THE 00Z CMC CONTINUES TO BE NOTICEABLY  
STRONGER WITH THIS, SO IT WAS NOT FAVORED IN THE LATE PERIOD BLEND  
FOR TODAY. FOR DAYS 6-7, THE WPC BLEND FAVORED NEARLY HALF OF THE  
ENSEMBLE MEANS TO HELP MITIGATE THE DIFFERENCES, WITH SOME  
DETERMINISTIC (MORE GFS AND ECMWF) SOLUTIONS FOR ADDED SYSTEM  
DEFINITION. THIS MAINTAINED GOOD CONTINUITY WITH THE PREVIOUS  
SHIFT AS WELL.  
 
   
..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. THE HEAT SHOULD FINALLY 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. GIVEN MUCH ABOVE NORMAL RAINFALL IN SOME LOCATIONS  
ACROSS THE SOUTHEAST, HEAVY RAINFALL MAY INCREASE THE FLOOD AND  
FLASH FLOOD THREAT, ESPECIALLY ACROSS PORTIONS OF THE SOUTHEAST ON  
FRIDAY WHERE WPC HAS A SLIGHT RISK HIGHLIGHTED ON THE EXPERIMENTAL  
DAY 5 ERO. BY THIS WEEKEND, A SURGE OF INCREASED MOISTURE WILL  
LIKELY ARRIVE FOR THE DESERT SOUTHWEST IN CONJUNCTION WITH  
TROPICAL STORM KAY WITH ADDITIONAL FLOODING CONCERNS. THERE REMAIN  
SOME TRACK UNCERTAINTIES WHICH OF COURSE HAS IMPLICATIONS FOR QPF  
ACROSS SOUTHERN CALIFORNIA AND THE SOUTHWEST. SEE THOSE PRODUCTS  
ISSUED BY THE NATIONAL HURRICANE CENTER FOR THE LATEST INFORMATION.  
 
SANTORELLI/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  
 
HAZARDS:  
- HEAVY RAIN ACROSS PORTIONS OF CALIFORNIA AND THE SOUTHWEST,  
SAT-SUN, SEP 10-SEP 11.  
- HEAVY RAIN ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY, THE  
TENNESSEE/OHIO VALLEY, THE  
MID-ATLANTIC, THE SOUTHERN APPALACHIANS, AND THE SOUTHEAST,  
THU-SUN, SEP 8-SEP 11.  
- FLOODING POSSIBLE ACROSS PORTIONS OF THE SOUTHERN APPALACHIANS  
AND THE TENNESSEE VALLEY.  
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE LOWER  
MISSISSIPPI VALLEY.  
- FLOODING LIKELY ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY.  
- EXCESSIVE HEAT ACROSS PORTIONS OF CALIFORNIA, THU-FRI, SEP 8-SEP  
9.  
- EXCESSIVE HEAT ACROSS PORTIONS OF THE NORTHERN/CENTRAL PLAINS,  
AND THE UPPER MISSISSIPPI VALLEY,  
THU, SEP 8.  
- HEAVY RAIN ACROSS PORTIONS OF THE ALASKA PANHANDLE AND MAINLAND  
ALASKA, THU-FRI, SEP 8-SEP 9.  
 
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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