240
FXUS02 KWNH 140728
PREEPD

Preliminary Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
326 AM EDT Mon Sep 14 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 portions of the
Northern/Central Plains, 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 Northern/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...

Models are in good agreement on the early medium range pattern,
including troughing over the Central U.S. and the evolution of the
Southern U.S. ridge. Most of the model spread lies with the
evolution of the Western U.S. troughing late this week through the
weekend as well as the closed mid-level disturbance retrograding
through the Florida Peninsula and into the Gulf. The AIGFS and
UKMET clustered well together through day 5 so were favored in the
blend. The AIGFS, Euro ensemble mean and GEFS mean clustered well
beyond day 5 and were thus favored in the blend through day 7.


...Weather/Hazards Highlights...

A potent low pressure system will bring another round of
thunderstorms and heavy rainfall to portions of the Central U.S.
later this week. Scattered showers and thunderstorms are expected
to redevelop over parts of Nebraska, South Dakota and the Upper
Midwest, where a slight risk (at least 15% chance) of excessive
rainfall is in effect on Thursday. This excessive rainfall threat
shifts eastward on Friday with a greater QPF signal over much of
the Upper Midwest/Great Lakes. Showers and thunderstorms spread
eastward into the Ohio Valley, Lower Great Lakes and Northeast this
weekend.

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




















$$