132  
FXUS02 KWBC 041857  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
256 PM EDT SUN SEP 04 2022  
 
VALID 12Z WED SEP 07 2022 - 12Z SUN SEP 11 2022  
 
...RECORD-SETTING HEAT WILL CONTINUE ACROSS THE WEST INTO THE  
NORTH-CENTRAL U.S. THROUGH THURSDAY AND MAY PERSIST IN CALIFORNIA  
THROUGH FRIDAY...  
 
   
..OVERVIEW
 
 
WIDESPREAD RECORD-BREAKING HEAT REMAINS A WEATHER HAZARD THROUGH  
THE MEDIUM RANGE PERIOD ACROSS CALIFORNIA THROUGH THE  
INTERMOUNTAIN WEST AND INTO THE NORTHERN HALF OF THE PLAINS  
THROUGH THURSDAY AS THE ANOMALOUS UPPER HIGH/RIDGE PERSISTS, WITH  
SOME GRADUAL MODERATION OF THE HEAT LATE IN THE WEEK. ACROSS THE  
EASTERN U.S., A BROAD UPPER TROUGH AND WEAK CLOSED LOW WILL BE IN  
PLACE, AND A COUPLE OF FRONTAL SYSTEMS AND GULF MOISTURE SHOULD  
ALLOW FOR RAIN AND THUNDERSTORMS IN THE SOUTHEAST AND POSSIBLY  
INTO THE OHIO VALLEY/GREAT LAKES REGIONS BY LATE WEEK. THEN THERE  
IS POTENTIAL FOR TROPICAL MOISTURE TO STREAM INTO THE SOUTHWEST  
OVER THE WEEKEND AS THE RECENTLY FORMED TROPICAL DEPRESSION  
TWELVE-E TRACKS NORTHWARD THROUGH THE EASTERN PACIFIC.  
 
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
WHILE THERE HAS ALWAYS BEEN GOOD MODEL AGREEMENT FOR THE LARGE  
UPPER HIGH/RIDGE CENTERED OVER THE INTERMOUNTAIN WEST, FORTUNATELY  
MODEL AGREEMENT HAS ALSO INCREASED CONSIDERABLY OVER THE LAST DAY  
OR SO WITH THE TIMING OF TROUGHING MOVING INTO THE NORTHWEST  
WEDNESDAY-THURSDAY AND TRACKING ACROSS THE NORTHERN TIER THROUGH  
NEXT WEEKEND, WHICH TEMPORARILY RESHAPES AND SUPPRESSES THE  
NORTHERN PART OF THE UPPER RIDGE. THERE ARE STILL CERTAINLY SOME  
DIFFERENCES IN TIMING AND THE EVOLUTION (AND POTENTIAL WIDENING)  
OF THE TROUGH AS ADDITIONAL ENERGY GETS INTEGRATED, BUT MORE ALONG  
THE LINES OF AVERAGE/TYPICAL DIFFERENCES FOR THE MEDIUM RANGE  
PERIOD RATHER THAN THE BELOW AVERAGE MODEL AGREEMENT AND THUS  
FORECAST CONFIDENCE FROM THE LAST SEVERAL CYCLES. THE ECMWF HAS  
THE MOST RUN-TO-RUN CONSISTENCY FOR THE TROUGH'S TIMING WHILE GFS  
RUNS HAVE WAFFLED, BUT THE 06Z GFS WAS IN GOOD ALIGNMENT WITH THE  
00Z ECMWF. THE 00Z UKMET AND CMC WERE A BIT SLOWER THAN THOSE  
MODELS AND THE 00Z ENSEMBLE MEANS, BUT IT DOES SEEM LIKE THE 12Z  
MODEL SUITE MAY BE A BIT SLOWER AS WELL FRIDAY-SUNDAY. THEN WHILE  
MODELS AGREE ON AN UPPER TROUGH/LOW WITH ITS AXIS ACROSS THE  
EAST-CENTRAL U.S. THROUGH LATE WEEK, THERE BECOMES SOME  
UNCERTAINTY WITH THE POSSIBLE COMBINATION OF THIS FEATURE AND THE  
INCOMING NORTHERN STREAM TROUGH. MODEL GUIDANCE AND THE FORECAST  
SHOWS SOME PHASING, WITH A TROUGH AXIS IN THE UPPER GREAT LAKES  
SOUTH-SOUTHWEST INTO THE LOWER MISSISSIPPI VALLEY BY DAY 7/SUNDAY,  
WITH THE UPPER RIDGE PERSISTING TO THE TROUGH'S WEST. THE WPC  
FRONTS/PRESSURES FORECAST UTILIZED A MULTI-MODEL DETERMINISTIC  
BLEND EARLY IN THE PERIOD, GRADUALLY INCLUDING AND INCREASING THE  
PROPORTION OF THE ECMWF MEAN AND EVENTUALLY SOME GEFS MEAN TO  
ABOUT HALF BY THE END OF THE PERIOD AS INDIVIDUAL MODEL  
DIFFERENCES INCREASED. THE FORECAST WAS FAIRLY CONSISTENT WITH  
CONTINUITY, WITH ONE CHANGE BEING INCREASED QPF IN THE GREAT LAKES  
AND OHIO VALLEY BY NEXT WEEKEND ALONG AND AHEAD OF THE COLD FRONT.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
CONSIDERABLY HOT TEMPERATURES PARTICULARLY BY SEPTEMBER STANDARDS  
ARE FORECAST TO CONTINUE INTO THROUGH WEDNESDAY AND THURSDAY FROM  
CALIFORNIA THROUGH THE GREAT BASIN INTO CENTRAL/NORTHERN PORTIONS  
OF THE ROCKIES AND HIGH PLAINS. DAYTIME HIGH AND OVERNIGHT/MORNING  
LOW TEMPERATURES OF 10-25F ABOVE AVERAGE WILL BE WIDESPREAD, WITH  
ACTUAL HIGHS OF 110+ 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. RECENT FORECASTS SHOW BETTER AGREEMENT FOR A  
SIGNIFICANT COOLING TREND BEHIND A COLD FRONT IN THE NORTH-CENTRAL  
U.S. ON FRIDAY, THOUGH CALIFORNIA IS LIKELY TO REMAIN HOT WITH THE  
REORIENTATION OF THE UPPER RIDGE ATOP THE REGION. BY NEXT WEEKEND,  
TEMPERATURES COULD BE WARMER THAN NORMAL ACROSS THE NORTHWEST  
SATURDAY INTO THE NORTHERN ROCKIES/HIGH PLAINS NEXT SUNDAY, BUT  
LIKELY NOT TO THE SAME ANOMALOUS LEVELS AS EARLIER IN THE WEEK.  
MEANWHILE, SLIGHTLY BELOW NORMAL HIGHS AND AROUND NORMAL LOWS ARE  
EXPECTED FOR THE LOWER MISSISSIPPI VALLEY AND SOUTHEAST GIVEN THE  
CLOUDY AND SHOWERY FORECAST. PARTS OF THE NORTHEAST/MID-ATLANTIC  
COULD SEE HIGHS THAT ARE BELOW NORMAL BY A FEW DEGREES ON  
WEDNESDAY, BEFORE GRADUALLY WARMING TO ABOVE NORMAL THROUGH THE  
LATTER PART OF THE WEEK.  
 
THE MAIN FOCUS FOR RAIN DURING THE PERIOD WILL BE ACROSS THE  
SOUTHEASTERN QUADRANT OF THE COUNTRY, AS AMPLE GULF MOISTURE FLOWS  
OVER A MEANDERING FRONTAL BOUNDARY NEAR THE GULF COAST WITH THE  
BROAD UPPER LOW IN THE VICINITY, PROMOTING SHOWERS AND  
THUNDERSTORMS. THERE MAY BE SOME FLOODING CONCERNS WITH  
SLOW-MOVING STORMS ACROSS THE GULF COAST, SOUTHEAST, AND INTO THE  
SOUTHERN APPALACHIANS. BY NEXT WEEKEND, MOISTURE COULD SPREAD  
FARTHER NORTH AHEAD OF A COLD FRONT TREKKING ACROSS THE GREAT  
LAKES AND OHIO VALLEY, AND THE RECENT FORECAST HAS RISEN RAINFALL  
TOTALS FOR THOSE AREAS. ADDITIONALLY, A SURGE OF INCREASED  
MOISTURE MAY ARRIVE IN THE SOUTHWEST IN CONJUNCTION WITH WHAT IS  
CURRENTLY TROPICAL DEPRESSION TWELVE-E.  
 
TATE  
 
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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