316  
FXUS02 KWBC 021953  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
352 PM EDT FRI SEP 02 2022  
 
VALID 12Z MON SEP 05 2022 - 12Z FRI SEP 09 2022  
 
...PROLONGED HEAT WAVE ACROSS MUCH OF THE WEST WILL LAST THROUGH  
THE MIDDLE OF NEXT WEEK...  
 
   
..OVERVIEW
 
 
A STRONG UPPER LEVEL HIGH WILL BE ANCHORED OVER THE CENTRAL GREAT  
BASIN THROUGH MUCH OF NEXT WEEK, PROMOTING CONTINUED EXCESSIVE  
HEAT ACROSS MUCH OF THE WEST AND INTO THE NORTHERN PLAINS THAT  
COULD BE RECORD BREAKING. THE HEAT WAVE IS EXPECTED TO GRADUALLY  
RECEDE ESPECIALLY ACROSS THE NORTHWEST DURING THE LATTER HALF OF  
NEXT WEEK AS AN ENERGETIC TROUGH COMES IN AND SUPPRESSES THE  
RIDGE/HIGH. MEANWHILE A BROAD UPPER TROUGH WITH EMBEDDED ENERGY  
WILL PERSIST ACROSS THE EAST, ALONG WITH A COUPLE OF FRONTAL  
BOUNDARIES THAT COULD ENHANCE CHANCES FOR RAIN AND THUNDERSTORMS,  
PARTICULARLY IN THE EASTERN U.S. ON MONDAY AND LINGERING IN  
SOUTHERN TEXAS THROUGH MUCH OF THE PERIOD. ADDITIONAL MOISTURE MAY  
APPROACH THE SOUTHWESTERN U.S. BY LATE NEXT WEEK STREAMING IN FROM  
A POSSIBLE TROPICAL SYSTEM TO THE SOUTH.  
 
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
GOOD MODEL AGREEMENT IS PRESENT AT THE BEGINNING OF THE PERIOD  
MONDAY WITH THE 594+DM UPPER HIGH AT 500MB AND THE HIGH REMAINING  
CENTERED AROUND THE CENTRAL GREAT BASIN THROUGH AT LEAST  
WEDNESDAY. THE DETAILS OF ITS SUPPRESSION BY THURSDAY-FRIDAY  
DEPEND ON THE FLOW FARTHER NORTH, SPECIFICALLY A STRONG SHORTWAVE  
TROUGH WITH A POTENTIAL EMBEDDED CLOSED LOW COMING INTO THE  
NORTHWEST WEDNESDAY-FRIDAY. THE 00Z/06Z MODEL SUITE THAT WAS  
AVAILABLE FOR THE WPC FORECAST HAPPENED TO BE PRETTY AGREEABLE  
WITH ITS TIMING AND THAT OF AN ASSOCIATED SURFACE LOW TRACKING  
ACROSS SOUTHERN CANADA. UNFORTUNATELY THE 12Z MODELS HAVE DIVERGED  
SOMEWHAT, WITH THE GFS MUCH WEAKER WITH THE SHORTWAVE, LEADING TO  
A FLATTER PATTERN, WHILE THE ECMWF SLOWED DOWN WITH THE SHORTWAVE,  
SO THIS IS STILL AN AREA OF UNCERTAINTY.  
 
MEANWHILE IN THE EAST, THERE IS GENERAL MODEL AGREEMENT FOR  
TROUGHING. EMBEDDED ENERGY AND THE DETAILS OF HOW THE TROUGHING IS  
ORIENTED AT ANY GIVEN TIME IS MUCH LESS CERTAIN FROM MODEL TO  
MODEL AND RUN TO RUN. THE ECMWF AND EC MEAN APPEARED MOST  
REASONABLE AND CONSISTENT FOR THE TROUGH, WITH THE GFS (ESPECIALLY  
THE 00Z) LIKELY TOO FAST TO MOVE TROUGHING OFFSHORE WEDNESDAY  
ONWARD. IT LOOKS LIKE IN THE 12Z MODEL SUITE THERE IS BETTER  
AGREEMENT FOR A CLOSED LOW SOMEWHERE IN THE EAST-CENTRAL U.S.  
THURSDAY-FRIDAY.  
 
THUS THE WPC FORECAST USED A MULTI-MODEL DETERMINISTIC BLEND EARLY  
IN THE PERIOD WITH A GRADUAL TRANSITION TOWARD MORE USAGE OF THE  
ENSEMBLE MEANS, ESPECIALLY THE ECENS MEAN, BY THURSDAY/FRIDAY.  
THIS BLEND ALLOWED FOR A STRONGER TROUGH AND SURFACE LOW IN THE  
NORTHWESTERN QUADRANT OF THE FORECAST DOMAIN THURSDAY-FRIDAY,  
THOUGH AS MENTIONED ABOVE THIS COULD CHANGE DUE TO THE NEWER  
GUIDANCE. CHANGES FROM THE NBM AND/OR CONTINUITY INCLUDE LOWERING  
QPF SOMEWHAT IN PARTS OF TEXAS GIVEN THE NBM'S HIGHER BIAS THAN  
THE BULK OF THE MODELS, AND FOLLOWING A MORE NORTHWARD/MORE INLAND  
TREND WITH QPF IN THE OHIO VALLEY TO NORTHEAST AS THE NBM AND  
MODELS AGREED ON THIS.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
CONSIDERABLY HOT TEMPERATURES PARTICULARLY BY EARLY SEPTEMBER  
STANDARDS ARE FORECAST TO CONTINUE THIS WEEKEND THROUGH LABOR DAY  
AND BEYOND FROM CALIFORNIA THROUGH THE GREAT BASIN INTO  
CENTRAL/NORTHERN PORTIONS OF THE ROCKIES AND HIGH PLAINS. HIGH AND  
LOW TEMPERATURES OF 10-20F ABOVE AVERAGE WILL BE WIDESPREAD  
THROUGH WEDNESDAY, AS ACTUAL TEMPERATURES OF 110+ ARE FORECAST FOR  
THE DESERT SOUTHWEST AND CALIFORNIA'S CENTRAL VALLEY WHILE  
WIDESPREAD 90S AND SOME 100S ARE EXPECTED ACROSS THE INTERMOUNTAIN  
WEST INTO THE NORTHERN HALF OF THE PLAINS. MULTIPLE DAILY RECORDS  
WILL BE SET, WITH SOME SEPTEMBER MONTHLY RECORDS POSSIBLE AS WELL.  
THE MAGNITUDE AND DURATION OF THE DANGEROUS HEAT WILL BOTH BE  
CONTRIBUTORS TO POTENTIAL SAFETY CONCERNS FOR SENSITIVE GROUPS  
SUCH AS THE ELDERLY, THOSE WORKING OUTSIDE, AND THOSE WITHOUT AIR  
CONDITIONING. TEMPERATURES ARE EXPECTED TO GRADUALLY MODERATE  
CLOSER TO NORMAL THURSDAY AND ESPECIALLY FRIDAY, THOUGH COULD  
STILL BE SLIGHTLY WARMER THAN AVERAGE ESPECIALLY ACROSS CALIFORNIA  
FRIDAY. MEANWHILE, SLIGHTLY BELOW NORMAL HIGHS AND AROUND NORMAL  
LOWS ARE EXPECTED FOR PORTIONS OF TEXAS INTO THE SOUTHEAST GIVEN  
THE CLOUDY AND SHOWERY FORECAST. PARTS OF THE NORTHEAST COULD SEE  
BELOW NORMAL HIGHS ONLY REACHING THE 60S OR LOW 70S ON LABOR DAY  
BEHIND A FRONT, BUT SHOULD GRADUALLY WARM TO ABOVE NORMAL THROUGH  
THE WEEK.  
 
A COLD FRONT PUSHING SOUTHWARD ACROSS THE NORTHEASTERN QUADRANT OF  
THE NATION WILL PROMOTE SHOWERS AND THUNDERSTORMS THERE ALONG WITH  
POTENTIALLY HEAVY RAINFALL AND FLOODING ON MONDAY AND POSSIBLY  
INTO TUESDAY, BEFORE CLEARING THERE AS THE FRONT PUSHES SOUTH.  
SEVERAL ROUNDS OF RAIN AND THUNDERSTORMS ARE POSSIBLE FOR SOUTHERN  
TEXAS WITH GULF MOISTURE PRESENT AND A STATIONARY FRONT IN ITS  
VICINITY. THE SOUTHEAST MAY SEE SCATTERED THUNDERSTORMS FOR THE  
FIRST HALF OF THE WEEK AND THESE MAY INCREASE IN COVERAGE BY THE  
LATTER PART OF THE WEEK, ESPECIALLY ALONG THE GULF COAST AND INTO  
THE SOUTHERN APPALACHIANS, BUT THERE ARE STILL SOME MODEL  
DIFFERENCES WITH THE DETAILS. BY THE END OF THE PERIOD, SOME  
INCREASED MOISTURE MAY ARRIVE IN THE SOUTHWEST IN CONJUNCTION WITH  
A TROPICAL SYSTEM TO THE SOUTH.  
 
TATE  
 
HAZARDS:  
- HEAVY RAIN ACROSS PORTIONS OF NEW ENGLAND, THE MID-ATLANTIC, AND  
THE APPALACHIANS, MON, SEP 5.  
- HEAVY RAIN ACROSS PORTIONS OF TEXAS, MON-WED, SEP 5-SEP 7.  
- FLOODING POSSIBLE ACROSS PORTIONS OF THE SOUTHERN PLAINS.  
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE LOWER  
MISSISSIPPI VALLEY AND THE SOUTHERN PLAINS.  
- FLOODING LIKELY ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY.  
- EXCESSIVE HEAT ACROSS PORTIONS OF THE NORTHERN PLAINS, THE  
NORTHERN ROCKIES, THE PACIFIC NORTHWEST, AND THE GREAT BASIN,  
MON-WED, SEP 5-SEP 7.  
- EXCESSIVE HEAT ACROSS PORTIONS OF CALIFORNIA AND THE SOUTHWEST,  
MON-THU, SEP 5-SEP 8.  
 
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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