343
FXUS02 KWBC 141929
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
329 PM EDT Mon Sep 14 2026

Valid 12Z Thu Sep 17 2026 - 12Z Mon Sep 21 2026


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


...Overview...

Anomalous upper ridging that has been supporting hazardous heat in
the South will gradually lose influence later this week, leading
to heatwave moderation. 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 itself will
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 East.
with frontal focus over the Mid- Atlantic/Northeast into next
weekend. Compact Atlantic closed upper low/trough southwestward
will track over Florida Thursday and then slowly westward across
the northern Gulf through this period. This feature may act to
organize Gulf convection and bring some marine/coastal threats.


...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 potent low pressure system will bring rounds 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 the Upper Midwest/Great
Lakes. Shower and thunderstorm focus should spread across the Ohio
Valley and Mid-Atlantic/Northeast over the weekend.

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

Mid-later week heat indices between 100-110 along with lows in the
mid-upper 70s will continue to produce widespread major to extreme
heat risk across the Southern Plains and Mid-Lower Mississippi
Valley. Some record high temperatures remain possible into late
week, but a weakening ridge should gradually moderate the heatwave
into the weekend.


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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