901
FXUS02 KWBC 121932
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
332 PM EDT FRI SEP 12 2025
VALID 12Z MON SEP 15 2025 - 12Z FRI SEP 19 2025
..OVERVIEW
THE FORECAST PERIOD SHOULD BEGIN WITH AN UPPER TROUGH/FRONTAL
SYSTEM SPREADING ENHANCED RAIN CHANCES FROM THE ROCKIES INTO THE
NORTHERN PLAINS AND EVENTUALLY UPPER MIDWEST. TROUGHING IN THE EAST
WITH THE POTENTIAL FOR A LINGERING CLOSED LOW WOULD BRING
INCREASING RAIN CHANCES ALONG AT LEAST COASTAL AREAS OF THE
CAROLINAS/SOUTHERN MID-ATLANTIC. UPPER RIDGING IN BETWEEN THESE
FEATURES SHOULD BRING ABOVE NORMAL TEMPERATURES TO THE MIDWEST AND
MISSISSIPPI VALLEY , WITH SOME AREAS WELL INTO THE 90S FOR HIGHS.
..GUIDANCE/PREDICTABILITY ASSESSMENT
LATEST MODEL GUIDANCE AT THE START OF THE MEDIUM RANGE PERIOD
(MONDAY SEPTEMBER 15) DEPICTS AN UPPER-TROUGH OVER THE EAST COAST
WITH POTENTIAL FOR A LINGERING UPPER-LOW IN THE GENERAL VICINITY OF
THE SOUTHEAST, AND AN UPPER-TROUGH WITH EMBEDDED SHORTWAVE
ENERGIES OVER THE NORTH-CENTRAL TO NORTHWESTERN U.S. STRONGER MEAN
UPPER- FLOW IS IN PLACE TO THE NORTH WITH AN UPPER- TROUGH OVER
NORTHEASTERN CANADA, UPPER-RIDGING OVER CENTRAL TO WESTERN CANADA,
AND AN UPPER- TROUGH OVER THE NORTHEASTERN PACIFIC. GUIDANCE IS
INITIALLY WELL CLUSTERED ON THE PROGRESSION OF FEATURES WITH THE
UPPER- TROUGH OVER THE NORTH- CENTRAL TO NORTHWESTERN U.S. SHIFTING
EAST AND UNDER THE RIDGE TO THE NORTH OVER CANADA LEADING TO AN AT
LEAST BRIEF REX BLOCK PATTERN. THE UPPER- TROUGH OVER THE
NORTHEASTERN PACIFIC SHOULD ALSO BEGIN TO DROP SOUTHEASTWARD
TOWARDS THE WEST COAST. GUIDANCE BEGINS TO SHOW INCREASING
UNCERTAINTY WITH RESPECT TO THE UPPER- LOW/ENERGY LINGERING OVER
THE GENERAL VICINITY OF THE SOUTHEAST/MID- ATLANTIC/OHIO VALLEY,
THROUGH MOST GUIDANCE GENERALLY AGREES IT WILL LINGER THROUGH AT
LEAST MID- NEXT WEEK, AND THEN SHEAR OUT/RETROGRADE A BIT WEST
AND/OR BE LIFTED NORTH AND THEN EASTWARD WITHIN THE MEAN UPPER-
FLOW FURTHER NORTH. THE SUITE OF AI MODELS FROM THE EC ACTUALLY
MAINTAINS THE UPPER-LOW IN POSITION/STRENGTH A BIT LONGER OVER THE
SOUTHEAST/MID- ATLANTIC IN COMPARISON TO THE OTHER
DETERMINISTIC/ENSEMBLE GUIDANCE. UNCERTAINTY ALSO INCREASES FOR THE
LATTER PART OF THE PERIOD WITH RESPECT TO THE EVOLUTION OF THE
SYSTEM OVER THE NORTH-CENTRAL U.S. AND INTERACTION WITH UPPER-
ENERGY TO THE NORTH, WITH THE MEANS RETAINING A WEAKENING UPPER-
WAVE. THE EC/CMC DETERMINISTIC/ENSEMBLE GUIDANCE ALONG WITH THE EC
AI MODEL SUITE ARE IN BETTER AGREEMENT WITH THE NORTHEASTERN
PACIFIC UPPER-TROUGH DIGGING SOUTHWARD ALONG THE WEST COAST BY THE
END OF THE PERIOD, WITH THE GFS/GEFS REMAINING MORE PROGRESSIVE AND
FURTHER NORTH.
THE UPDATED WPC FORECAST BEGAN WITH A BLEND OF THE ECMWF/GFS/CMC
GIVEN GOOD GENERAL AGREEMENT EARLY IN THE PERIOD. INCLUDED AN
INCREASED CONTRIBUTION FROM THE ENSEMBLE MEANS DURING THE MIDDLE
PART OF THE PERIOD DUE TO THE LACK OF AGREEMENT ON THE DETAILS WITH
REGARDS TO THE SOUTHEASTERN U.S. UPPER-LOW, PARTICULARLY GIVEN THE
THE NOTABLE DIFFERENCE IN THE AI GUIDANCE COMPARED TO THE
AVAILABLE DETERMINISTIC GUIDANCE. THE LATTER PART OF THE FORECAST
RELIES ON THE ECENS/CMC ENSEMBLE MEANS AND ECMWF/CMC WHICH ARE
BETTER CLUSTERED WITH RESPECT TO MAIN NORTHERN STREAM DEEPENING
UPPER-TROUGH/LOW OVER NORTHEASTERN CANADA AND UPPER-TROUGH DIGGING
OVER THE WEST COAST COMPARED TO THE GFS/GEFS. OTHER SMALLER SCALE
DETAILS IN BETWEEN OVER THE CENTRAL U.S. ARE HARDER TO RESOLVE AT
THIS TIME AND HANDLED BY A RELIANCE ON A SIGNIFICANT INCREASE IN
THE ENSEMBLE MEANS TO MAINTAIN AT LEAST WEAK, MEAN UPPER-TROUGHING.
..WEATHER/HAZARDS HIGHLIGHTS
INTO EARLY NEXT WEEK, MOISTURE CONVERGING NEAR A COASTAL FRONT/
TROUGH NORTH OF A WAVY FRONTAL SYSTEM FARTHER OFFSHORE COULD
PRODUCE ENHANCED RAIN NEAR OR JUST OFFSHORE THE CAROLINAS AND
VICINITY. POTENTIAL FOR AN UPPER-LOW IN THE VICINITY WOULD MAINTAIN
AT LEAST LIGHT TO MODERATE RAINFALL CHANCES THROUGH MID- WEEK,
INCLUDING FURTHER INLAND. MEANWHILE, THE TRAILING PORTION OF THE
STATIONARY FRONT WILL BE CLOSE ENOUGH TO BRING SOME SHOWERS AND
EMBEDDED THUNDERSTORMS INTO THE SOUTHERN FLORIDA PENINSULA EARLY
NEXT WEEK. HOWEVER, AS THE UPPER LOW NEAR THE EAST COAST BEGINS TO
WEAKEN AND/OR LIFT NORTHWARD LATE NEXT WEEK, TROPICAL MOISTURE FROM
THE CARIBBEAN SEA APPEARS TO LIFT NORTHWARD AND BRING MORE
WIDESPREAD SHOWERS AND THUNDERSTORMS INTO SOUTH FLORIDA UNDER THE
INFLUENCE OF A SUBTROPICAL JET STREAM.
TO THE WEST, AN UPPER TROUGH WILL SPREAD ANOTHER ROUND OF
PRECIPITATION EASTWARD ACROSS THE NORTHERN ROCKIES MONDAY-TUESDAY,
INTO THE PLAINS TUESDAY-THURSDAY, AND INTO THE UPPER MIDWEST
THURSDAY- FRIDAY. PORTIONS OF THE NORTH- CENTRAL PLAINS APPEAR TO
HAVE THE HIGHEST CHANCE OF STRONG THUNDERSTORMS WITH HEAVY
DOWNPOURS LATE TUESDAY INTO EARLY WEDNESDAY AS THE UPPER TROUGH
INTERACTS WITH A SURFACE FRONT. A MARGINAL RISK OF FLASH FLOODING
HAS BEEN MAINTAINED ON DAY 5 FOR THAT AREA. ELSEWHERE, SOME
MONSOONAL MOISTURE IS FORECAST TO REACH THE SOUTHWEST, PRIMARILY
NEW MEXICO MONDAY- WEDNESDAY AND THEN THE DESERT SOUTHWEST BY LATE
WEEK.
AN UPPER-RIDGE WILL PROMOTE HOT TEMPERATURES CENTERED ON THE
MIDWEST/MISSISSIPPI VALLEY THROUGH AT LEAST MID-NEXT WEEK, WITH
ANOMALIES OF 10-20 DEGREES ABOVE AVERAGE. TEMPERATURES WELL IN THE
90S WILL BE COMMON, AND A HANDFUL OF RECORD HIGHS ARE POSSIBLE BUT
CURRENTLY DO NOT LOOK TO BE WIDESPREAD. RECENT MODEL TRENDS
CONTINUE TO FAVOR SOME WARMER THAN AVERAGE TEMPERATURES TO MOVE
INTO THE NORTHEAST AS THE WEEK PROGRESSES. INITIALLY COOLER THAN
AVERAGE TEMPERATURES IN THE NORTHWEST LOOK TO MODERATE AS THE WEEK
PROGRESSES.
PUTNAM/KONG
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 (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
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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