165
FXUS02 KWBC 120704
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
304 AM EDT Sat Sep 12 2026

Valid 12Z Mon Sep 14 2026 - 12Z Fri Sep 18 2026


...Hazardous heat continues over the Southern Plains as heavy rain
and severe weather threaten the Middle/Upper Mississippi Valley and
Upper Great Lakes early next week...


...Overview...

An upper-level ridge will retrograde from the Southeast into the
Central U.S. next week. This ridge will initially generate
hazardous heat in the Southern Plains before reinvigorating monsoon
storms capable of producing flash flooding over parts of the
Southwest mid-to-late week. Zonal to diffluent flow across the
northern tier will support heavy rainfall and potentially severe
weather across portions of the Middle/Upper Mississippi Valley and
Upper Great Lakes early-to-mid week.


...Guidance/Predictability Assessment...

Models are generally in good agreement on the evolution of the
Southern ridge, while uncertainty continues to plague the West
Coast pattern. Some models signal an elongated trough swinging
through the West and Central U.S. next week, whereas another camp
of models suggest a split flow with energy detaching from the
parent low, which swings across the northern tier, and sits over
the Northwest late next week.

A blend consisting of the deterministic GFS/ECMWF and their
respective Ai models was utilized on day 3 before replacing the GFS
with the GEFS on day 4 due to better clustering around a split flow
solution over the West being depicted by the favored blend. The
ensemble means are gradually increased through the rest of the
period due to the timing and amplitude uncertainties surrounding
the Western U.S. trough evolution mid-to-late week.


...Weather/Hazards Highlights...

A potent low pressure system will move through the northern tier
beginning on Monday. Anomalous moisture associated with this
system will generate a multi-day heavy rainfall threat, with an
isolated to scattered flash flood threat possible from the Central
Plains to the Upper Great Lakes on Tuesday and Wednesday in
particular. Slight risks (at least 15% chance) of excessive
rainfall are in effect for portions of the aforementioned areas.
There`s also the threat of severe weather from eastern Nebraska
through Iowa and into southeastern Minnesota and southwestern
Wisconsin, where a slight risk (level 2/5) of severe weather is in
effect.

A strong ridge (potentially a record max for mid-September per the
NAEFS ESAT) over the South and Southeast will generate well above
average temperatures across the Central/Southern Plains and into
the Lower Mississippi Valley/Mid-South next week. Heat indices
between 100-110 degrees may support major to locally Extreme
HeatRisk over portions of the aforementioned areas between Monday
and Wednesday. Temperatures moderate beginning on Thursday.

The return of the Central U.S. ridge should reinvigorate monsoonal
storms across the Southwest beginning early next week. Moist
southerly flow into the Southwest could produce isolated instances
of flash flooding across portions of eastern Arizona through much
of New Mexico. Burn scars, dry washes and slot canyons are
especially sensitive to any heavy rainfall that occurs.
Additionally, persistent easterly flow across the Florida
Peninsula along with an embedded weak upper low/trough will
increase rainfall chances across the southern half of the state,
as well as, specifically the urban corridor of Southeast Florida.


Kebede/Snell


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












$$