878
FXUS02 KWBC 151855
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
255 PM EDT Tue Sep 15 2026

Valid 12Z Fri Sep 18 2026 - 12Z Tue Sep 22 2026


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


...Overview...

An anomalous ridge which supported a heat wave in the Southern
Plains and Lower Mississippi Valley will weaken considerably under
the influence of an amplifying upstream trough as well as a closed
mid-level disturbance moving into the northeast Gulf later this
week. The upstream trough will produce heavy rainfall across
portions of the Northern Plains, Upper Midwest/Great Lakes and
Northeast this weekend. Meanwhile, the passage of the Central U.S.
trough should reduce heavy rainfall concerns over the
Southwest/Southern Plains this weekend before an East Pacific
disturbance renews monsoonal storms across the region early next
week.


...Guidance/Predictability Assessment...

Latest guidance is in fairly good agreement on the large scale
pattern evolution through the period, but with some notable
differences in the details of various systems. The large upper low
moving across Florida and into the Gulf this weekend shows some
uncertainty in strength and how long it lingers across the
northeast Gulf before weakening. The main outlier with the
shortwave into the Upper Midwest this weekend is the CMC which
becomes out of phase with the consensus by early next week as
energy gets leftover across the West and entrained in another
system across the West. A deeper trough moving towards the
Northwest late period shows ok agreement, with the exception of the
GFS which was quite a bit faster.

The WPC forecast today used a blend of the deterministic guidance,
more heavily weighted towards the ECMWF and EC-AIFS early period,
before transitioning to a 50/50 blend of the EC/EC-AIFS with the
ensemble means.


...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 the Upper Midwest, where a slight risk (at least 15
percent chance) of excessive rainfall is in effect on Friday.
Thunderstorms and heavy rainfall focus should spread across the
Great Lakes, Ohio Valley and Northeast over the weekend, before
dropping south into the Mid- Atlantic early next week.

Shortwave disturbances streaming north through the
Southwest/Southern Plains will generate a little bit more
convection over New Mexico on Friday before an amplifying trough
shifts the unsettled weather into the Central/Southern Plains this
weekend. An East Pacific trough moving into the Southwest should
reignite monsoonal moisture across New Mexico by early next week.
Slot canyons and dry washes are especially susceptible to flash
flooding from any storms that develop.

Hazardous heat will continue to be a concern across parts of the
South and Lower Mississippi Valley/Tennessee Valley late this week
and into the weekend with major to extreme HeatRisk and some record
high temperatures. The heatwave across this region should finally
moderate by Sunday and especially next week as the upper level
ridge weakens.


Santorelli/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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