942
FXUS02 KWBC 130744
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
344 AM EDT Sun Sep 13 2026

Valid 12Z Tue Sep 15 2026 - 12Z Sat Sep 19 2026


...Hazardous heat subsides over the Southern Plains as heavy rain
threatens the Central Plains, Middle/Upper Mississippi Valley and
Southwest...


...Overview...

An upper ridge, which has recently produced hazardous heat in the
South, will weaken later this week, leading to a moderation in
temperatures across the Central and Southern U.S.. This ridge will
also be responsible for pulling up a continuous stream of mid-level
vorticity lobes from Mexico, which in turn will generate monsoon
storms in the Southwest. Persistent diffluence over the North-
Central U.S. will support heavy rainfall for portions of the
Central Plains and Middle/Upper Mississippi Valley.


...Guidance/Predictability Assessment...

Models are in relatively good agreement on the overall synoptic
pattern evolution across the lower 48 during the medium range
period. The timing and amplitude of a second shortwave entering
the Northwest as well as it`s evolution through the Central U.S. by
next weekend carries some uncertainty.

A general model blend consisting of the deterministic and Ai models
are used through day 4. The ensemble means are introduced on day 5
to mitigate some of the uncertainty associated with the
Western/Central U.S. trough. The Ai models are favored in the blend
due to consistent clustering between the ECAIFS and AIGFS.


...Weather/Hazards Highlights...

A quasi-stationary front 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 slight risks (at least 15% chance) of excessive rainfall are
in effect between Tuesday and Thursday.

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. Slight
risks of excessive rainfall are in effect from eastern Arizona into
much of 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 across the
Southern Plains beginning on Thursday. Showers and thunderstorms
work their way into the Eastern U.S. beginning on Thursday and
continuing into the weekend.


Kebede


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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