160
FXUS02 KWBC 121944
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
344 PM EDT Sat Sep 12 2026

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


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


...Overview...

An upper-level ridge/closed high will retrograde from the
Southeast to the south-central U.S. next week. This ridge will
support hazardous heat across the Southern Plains into later next
week before finally moderating. Meanwhile, monsoon storms capable
of producing flash flooding will reinvigorate over parts of the
Southwest as moisture is channeled between the ridge and a western
U.S. mean upper trough. 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 vicinity
with frontal interction, but supporting shortwave timing/details
remains uncertain in guidance. Western Atlantic upper/surface
trough approach and passage across Florida into the northern Gulf
also has potential to focus convection to monitor later next week.

...Guidance/Predictability Assessment...

Medium-range guidance clustering has improved over the last few
guidance cycles, but especially with the latest 06/12 UTC runs to
bolster forecast confidence. A guidance blend with slightly more
ensemble means/machine learning guidance emphasis later period
seems to offer a consistent forecast basis for threat messaging.

...Weather/Hazards Highlights...

A potent low pressure system will lift over southern Canada to
Hudson Bay on Tuesday. The guidance signal has increased that
anomalous moisture lifting into this system and pooling into a
slowing trailing front will fuel a multi-day strong convective and
heavy rainfall/flash flooding threat from the Central Plains and
Mid-Mississipppi Valley to the Great Lakes Tuesday and Wednesday.
Marginal and embedded Slight Risk threat areas are depicted on the
WPC Excessive Rainfall Outlook (ERO) as linked below.

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 into next
midweek. Temperatures should moderate beginning on Thursday.

The return of the Central U.S. ridge and emerging mean upper
troughing into the West should provide a moisture conduit to
reinvigorate monsoonal storms across the Southwest next week.
Moist southerly flow into the Southwest could produce isolated
instances of flash flooding from eastern Arizona through southeast
Utah and New Mexico into the central Rockies. Burn scars, dry
washes and slot canyons are especially sensitive to any heavy
rainfall that occurs. The ERO maintains a Marginal Risk area.

Additionally, moist onshore Atlantic flow over Florida along with
southwestard passage of an upper low/trough will increase and
maintain rainfall chances next week and subsequent emergence over
the northern Gulf could support organized convection to monitor.

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














$$