122
FXUS02 KWBC 091943
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
343 PM EDT WED SEP 9 2026
VALID 12Z SAT SEP 12 2026 - 12Z WED SEP 16 2026
...PROLONGED LATE-SUMMER HEAT WAVE LINGERS FOR THE SOUTHERN PLAINS
INTO EARLY NEXT WEEK...
..OVERVIEW
A SHORTWAVE WILL PUSH A COLD FRONT FROM THE UPPER MIDWEST TO THE
NORTHEAST THIS WEEKEND, WITH INCREASING RAIN CHANCES ALONG AND
AHEAD OF IT. BEHIND THIS, A COMPACT CLOSED LOW WILL MOVE INTO THE
NORTHWEST BY SATURDAY, PROGRESSING EASTWARD INTO THE NORTHERN
PLAINS BY MONDAY. MODERATE TO HEAVY RAINFALL LOOKS INCREASINGLY
LIKELY ACROSS THE UPPER MISSISSIPPI VALLEY TO GREAT LAKES SUNDAY
AND MONDAY, WITH SOME WINTER WEATHER POTENTIAL FOR THE NORTHERN
ROCKIES. MEANWHILE, UPPER LEVEL RIDGING WILL PERSIST ACROSS THE
SOUTHERN TIER, MAINTAINING HOT CONDITIONS FOR MAINLY THE SOUTHERN
PLAINS AND MONSOONAL MOISTURE FOR THE SOUTHWEST. ANOTHER
POTENTIALLY DEEPER SHORTWAVE MOVES INTO THE NORTHWEST NEXT TUESDAY
OR WEDNESDAY.
..GUIDANCE/PREDICTABILITY ASSESSMENT
WHILE THE GUIDANCE WAS GENERALLY AGREEABLE ON THE OVERALL PATTERN
THROUGH THE PERIOD THERE WERE SOME NOTABLE TIMING/EVOLUTION
DIFFERENCES ON THE MAIN FEATURES. AN INITIAL UPPER-TROUGH OVER
SOUTH-CENTRAL CANADA AND ALONG THE NORTHERN TIER OF THE U.S. WILL
PROGRESS EASTWARD TOWARDS THE EAST COAST THROUGH THE WEEKEND. THE
GUIDANCE IS INITIALLY AGREEABLE ON THE PROGRESSION BEFORE THE CMC
AND TO A LESSER DEGREE THE AI GUIDANCE SHOWS THE UPPER-TROUGH
AMPLIFYING ALONG THE EAST COAST. THE GFS/ECMWF/UKMET AND ECENS/GEFS
MEANS DO NOT SHOW THIS AMPLIFICATION AND MAINTAINED BROADER
RIDGING ACROSS THE SOUTHEASTERN U.S. INTO THE SOUTHWEST ATLANTIC.
MEANWHILE, UPSTREAM, GUIDANCE AGREES ANOTHER UPPER-WAVE WILL DROP
SOUTHWARD INTO THE INTERIOR WEST AND AMPLIFY AS A CLOSED LOW
DEVELOPS INTO THE WEEKEND. ALL GUIDANCE IS ALSO IN AGREEMENT THE
UPPER-LOW WILL THEN LIFT NORTHEASTWARD ACROSS THE CENTRAL/NORTHERN
PLAINS AND OPEN INTO A WAVE OVER THE MIDWEST EARLY TO MID-NEXT
WEEK. HOWEVER, THE SAME GUIDANCE CAMPS THAT DIFFERED ON THE
AMPLIFICATION TO THE EAST ALSO DIFFER ON THE EVOLUTION OF THIS
FEATURE. THE GFS/ECMWF/UKMET ARE MORE AMPLIFIED OVER THE WESTERN
U.S. AND THEN BRING THE OPENING WAVE/ACCOMPANYING SURFACE SYSTEM
ACROSS THE PLAINS AND THROUGH THE MIDWEST FASTER THAN THE CMC AND
AI GUIDANCE. THE GEFS/ECENS MEANS FAVOR THE FASTER PROGRESSION OF
THE GFS/ECMWF/UKMET INITIALLY BEFORE SLOWING AS THE SYSTEM
PROGRESSES INTO CANADA. ALL GUIDANCE ALSO AGREES ANOTHER UPSTREAM
UPPER-WAVE WILL FOLLOW INTO THE NORTHWESTERN U.S. BY MID- WEEK
THOUGH AGAIN DIVERGE ON PROGRESSION WITH THE CMC FASTER THAN THE
GFS/ECMWF.
THE UPDATED WPC FORECAST FAVORED A BLEND OF THE GFS/ECMWF/UKMET
THROUGH THE EARLY PART OF THE PERIOD GIVEN THEIR SOLUTIONS BETTER
FELL WITHIN THE ENVELOPE OF THE MEANS AND MAINTAINED BETTER WPC
FORECAST CONTINUITY. A 50% CONTRIBUTION OF THE ECENS/GEFS MEANS IS
INCLUDED FOR THE LATTER PART OF THE PERIOD AS THE TIME-LIMITED
UKMET IS REMOVED AND THE ECMWF/GFS START TO PROGRESS A BIT FASTER
WITH THE SYSTEM OVER THE MIDWEST AS IT MOVES INTO CANADA. THE NBM
LOOKED LIKE A REASONABLE STARTING POINT WITH ONLY MINIMAL
ADJUSTMENTS MADE TO LOWER TEMPERATURES A BIT FOLLOWING PREFERRED
FRONTAL PROGRESSION OVER THE INTERIOR WEST AND THEN ALONG THE
NORTHERN TIER. THE QPF FORECAST ALSO LOOKED REASONABLE WITH THE
FOOTPRINT/AMOUNTS IN LINE WITH THE PREFERRED ENSEMBLE MEANS AND
DETERMINISTIC GUIDANCE, PARTICULARLY WITH RESPECT TO HEAVIER
RAINFALL EXPECTED OVER THE UPPER MIDWEST DURING THE SUNDAY TO
MONDAY TIMEFRAME.
..WEATHER/HAZARDS HIGHLIGHTS
HEAT WILL REMAIN IN THE FORECAST INTO THE MEDIUM RANGE PERIOD
ACROSS MUCH OF THE SOUTHERN TIER OF THE COUNTRY WITH BROAD UPPER-
RIDGING IN PLACE. THE GREATEST COVERAGE OF MODERATE TO EXTREME HEAT
RISK WILL FOCUS ON THE SOUTHERN PLAINS/TEXAS INTO THE LOWER
MISSISSIPPI VALLEY. THIS SOUTHERN RIDGE WILL ALSO HELP SUPPORT
MONSOONAL MOISTURE AND DAILY SHOWER AND THUNDERSTORM CHANCES FOR
THE FOUR CORNERS REGION MUCH OF THE PERIOD. THERE LOOKS TO BE AN
UPTICK IN THE INFLUX OF MOISTURE EARLY NEXT WEEK AS THE SOUTHERN
RIDGE SHIFTS EASTWARD WITH A GREATER CHANCE FOR LOCALLY HEAVY
RAINFALL/FLASH FLOODING.
A LINGERING FRONT OVER THE SOUTHEAST AND MID-ATLATIC STATES WILL
CONTINUE A DAILY THREAT FOR SHOWERS AND THUNDERSTORMS, WITH LOCALLY
HEAVY RAIN POSSIBLE PARTICULARLY ACROSS THE PIEDMONT SATURDAY.
ANOTHER FRONT WILL BRING RAIN FROM THE CENTRAL U.S. INTO THE
NORTHEAST, WITH SOME ELEVATED FLASH FLOOD THREAT ACROSS PARTS OF
THE CENTRAL PLAINS TO MID- MISSISSIPPI VALLEY ON SATURDAY. THE MAIN
FOCUS FOR PRECIPITATION DURING THE PERIOD THOUGH WILL BE ACROSS
THE NORTHWEST INTO THE NORTHERN U.S. THIS WEEKEND AND EARLY NEXT
WEEK AS AN UPPER LOW MOVES THROUGH. A STRONG COLD FRONT WILL
ENHANCE RAINFALL CHANCES AHEAD OF IT, WITH MODERATE TO HEAVY
RAINFALL POTENTIAL INCREASING ESPECIALLY INTO SUNDAY AND MONDAY
ACROSS PORTIONS OF THE PLAINS INTO THE MIDWEST. ADDITIONAL HEAVY
RAINFALL IS LIKELY TO THE WEST UNDER THE CORE OF THE UPPER-LOW
ACROSS THE NORTHERN HIGH PLAINS OF MONTANA SUNDAY. WINTRY WEATHER
WILL ALSO BE POSSIBLE IN THE NORTHERN ROCKIES THIS COMING WEEKEND
AS COOLER AIR MOVES IN BEHIND THE COLD FRONT. SHOWERS WILL MOVE
WITH THE FRONT INTO THE OHIO VALLEY AND NORTHEAST EARLY NEXT WEEK.
PUTNAM/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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