342
FXUS02 KWBC 131855
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
255 PM EDT Sun Sep 13 2026

Valid 12Z Wed Sep 16 2026 - 12Z Sun Sep 20 2026


...Hazardous Heat subsides over the South-Central U.S. mid-late
week as heavy rain/strong thunderstorms threaten the Central
Plains, Middle/Upper Mississippi Valley and Southwest...


...Overview...

Upper ridging that has been supporting hazardous heat in the South
will weaken later this week, leading to some moderation in
temperatures across the Central and Southern U.S.. Flow between
the ridge and digging trough energy over the West will meanwhile
provide a moisture channel as a stream of mid-level vorticity
lobes lift from Mexico. This will generate monsoon storms from the
Southwest through the South-Central Rockies. Trough development
over the West has improved guidance support to provide cooling and
unsettled conditions, but limited precipitation. Persistent
diffluence and frontal system moisture/instability pooling will
support a multi-day threat for heavy rainfall/flash flooding for
the Central Plains and Middle/Upper Mississippi Valley. Frontal
system progression should also spread chances for showers and
thunderstorms into the Eastern U.S. late week into next weekend.
There is also a consistent guidance signal to bring a compact
Atlantic closed upper low/trough southwestward over Florida
Thursday and then slowly westward across the northern Gulf
Friday/next weekend. This feature may act to organize Gulf
convection and associated marine and coastal threats to monitor.

...Guidance/Predictability Assessment...

Guidance clustering has improved to bolster forecast confidence,
but some flow embedded system timing differences remain. Favor a
multi-model and ensemble mean/machine learning guidance composite
to mitigate variance as consistent with individual predictability.
This provides a consistent forecast basis for threat messaging.

...Weather/Hazards Highlights...

A quasi-stationary front/baroclinic zone draped across the Central
Plains and Middle/Upper Mississippi Valley will act as a focus for
anomalous moisture to generate a multi-day heavy rainfall event
beginning on Tuesday. Scattered to isolated thunderstorms are also
anticipated along the front. The axis of heaviest rainfall is
likely to occur between eastern Kansas/Nebraska into northern and
western Illinois, where WPC Excessive Rainfall Outlook (ERO) Slight
risk areas are in effect Tuesday-Thursday. The threat may then
lift to the Upper Midwest/Great Lakes Friday/Saturday to monitor.

Meanwhile, lobes of shortwave vorticity streaming north out of
Mexico should interact with anomalous moisture and modest instability
to generate monsoon storms across the Southwest this week. ERO Slight
risks areas are in place from eastern Arizona to New Mexico
through this Thursday. Slot canyons and dry washes are especially
susceptible to flash flooding from any storms that develop.

On Wednesday, heat indices between 100-110 along with lows in the
mid-to-upper 70s will produce widespread major to extreme heat
risk across the Southern Plains and Lower Mississippi Valley. A
weakening ridge will support moderating temperatures later week.

Kebede/Schichtel


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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