569
FXUS02 KWNH 040642
PREEPD
PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
241 AM EDT FRI SEP 4 2026
VALID 12Z MON SEP 07 2026 - 12Z FRI SEP 11 2026
...DANGEROUS LATE-SUMMER HEAT WAVE LINGERS FOR THE CENTRAL/
SOUTHERN PLAINS TO THE MID/LOWER MISSISSIPPI VALLEY INTO EARLY NEXT
WEEK...
..OVERVIEW
A STRONG UPPER RIDGE OVER THE CENTRAL U.S. THIS WEEKEND WEAKENS
AND SUPPRESSES SOUTH TO THE ENTIRE SOUTHERN TIER THROUGH THE MIDDLE
OF NEXT WEEK, CONTINUING A DANGEROUS AND LONG DURATION HEAT WAVE
FOR THE SOUTH-CENTRAL US. MEANWHILE, AN UPPER LOW OVER THE
NORTHWEST ON MONDAY WILL ROUND THE TOP OF THIS RIDGE, EVENTUALLY
INTO THE NORTHERN GREAT LAKES/NORTHEAST BY LATER IN THE WEEK. THIS
SYSTEM BRINGS A THREAT FOR HEAVY RAINFALL ACROSS THE NORTHERN
PLAINS TO UPPER MIDWEST EARLY IN THE WEEK, WITH SHOWERS INTO THE
NORTHEAST MID TO LATE WEEK. ANOTHER SYSTEM DROPS DOWN THE WEST
COAST AROUND WEDNESDAY, POSSIBLY COMBINING WITH ENERGY AND MOISTURE
FROM HURRICANE MARIE, CREATING A VERY UNCERTAIN WESTERN U.S.
FORECAST BY LATE PERIOD.
..GUIDANCE/PREDICTABILITY ASSESSMENT
GUIDANCE IS FAIRLY AGREEABLE EARLY PERIOD WHICH FEATURES A COMPACT
UPPER LOW THROUGH THE NORTHERN TIER ACTING TO SUPPRESS THE
SOUTHERN U.S. RIDGE A BIT. TIMING WITH THIS SYSTEM BECOMES MORE
QUESTIONABLE MID TO LATE PERIOD AS IT MOVES INTO THE GREAT
LAKES/NORTHEAST REGION WITH THE GFS AND CMC FASTER THAN THE ECMWF
AND EC-AIFS GUIDANCE. HOWEVER, A SECOND SYSTEM DROPPING DOWN THE
WEST COAST MID-PERIOD, WITH POTENTIAL INTERACTION WITH CURRENT
HURRICANE MARIE IN THE EASTERN TROPICAL PACIFIC IS WHAT DROVE THE
MODEL PREFERENCES, ESPECIALLY FOR THE SECOND HALF OF THE PERIOD.
THE GFS AND CMC WERE MOST AGGRESSIVE WITH THIS SCENARIO, WITH A
FAIRLY DEEP UPPER LOW DEVELOPING OFF THE WEST COAST BY THE END OF
THE WEEK. THE ECMWF AND EC-AIFS SOLUTIONS WERE CLOSER TO THAT OF
THE ENSEMBLE MEANS SHOWING A BIT WEAKER SOLUTION AND MORE
SEPARATION BETWEEN WHATEVER ENERGY IS LEFT OF MARIE AND THE WEST
COAST SHORTWAVE. THE WPC FORECAST BLEND WAS BASED MORE HEAVILY ON
THE ECMWF AND EC-AIFS SOLUTIONS, WITH MORE INCORPORATION OF THE
ENSEMBLE MEANS BY LATE PERIOD.
..WEATHER/HAZARDS HIGHLIGHTS
THE LONG DURATION AND DANGEROUS HEAT WAVE SHOULD FOCUS OVER THE
MID/LOWER MISSISSIPPI VALLEY TO SOUTHERN TEXAS BY EARLY NEXT WEEK,
THOUGH WIDESPREAD EXTREME HEATRISK CONTINUES INTO THE SOUTH-CENTRAL
PLAINS DUE TO VERY WARM OVERNIGHT LOW TEMPERATURES PRIMARILY. KEY
MESSAGES REMAIN IN EFFECT, THOUGH THE GREATER CONCERN FOR NOW IS
INTO THE WEEKEND/SHORT RANGE WITH LESS CERTAINTY ABOUT HOW EXTREME
THE TEMPERATURES WILL BE FOR THE FIRST PART OF NEXT WEEK.
MEANWHILE, COOLER TEMPERATURES OVER THE OHIO VALLEY, MID- ATLANTIC,
AND SOUTHEAST LINGER THROUGH LABOR DAY BEFORE UNCERTAINTY REIGNS
AS TO THE POSITION OF THE NORTHERN EXTENT OF THE SOUTHERN RIDGE
AXIS. COOLER THAN NORMAL TEMPERATURES WILL ALSO PERSIST FOR MUCH OF
THE WESTERN U.S. FOR EARLY NEXT WEEK UNDER THE TROUGH AND
POTENTIALLY LASTING THROUGH NEXT WEEK DEPENDING ON THE TROUGH AXIS
POSITION.
THE UPPER LOW THROUGH THE NORTHERN TIER WILL BRING SOME EARLY WEEK
HEAVY RAINFALL THREATS FROM THE NORTHEAST PLAINS INTO THE UPPER
MIDWEST. RAINFALL WILL CONTINUE TO ACCOMPANY THIS SYSTEM AS IT
SLIDES THROUGH THE GREAT LAKES AND NORTHEAST AS WELL. MONSOONAL
MOISTURE WILL CONTINUE INTO THE SOUTHWEST, WITH EXPANDING MOISTURE
THREATS AS TROUGHING DEVELOPS OVER THE WEST WITH ENHANCED TROPICAL
MOISTURE FROM HURRICANE MARIE. UNCERTAINTY REMAINS HIGH ON AMOUNTS
AND COVERAGE ACROSS THE WEST LATER NEXT WEEK.
SANTORELLI
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 FORECAST, EXCESSIVE RAINFALL OUTLOOK,
WINTER WEATHER OUTLOOK PROBABILITIES, HEAT INDICES AND KEY MESSAGES
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
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW
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