Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
253 PM EDT Fri Aug 14 2026

Valid 12Z Mon Aug 17 2026 - 12Z Fri Aug 21 2026


...Long-duration heat wave continues across the South/Southeast...

...Midwest Heavy Rain/Flooding Threat renews Tuesday/Wednesday...


...Overview...

Ample southern tier U.S. upper ridging should be well established
into next week and bring more hazardous heat to the south-central
U.S. and Southeast. To the north of the ridge, relatively active
flow will produce rounds of rain and thunderstorms across the U.S.
northern tier. In this pattern, rainfall amounts are forecast to
peak in the Midwest Tuesday and the Great Lakes Wednesday, along
with local strong to severe convection and flash flooding threats.
Additionally, some monsoonal moisture coming north under the ridge
will allow for convection in the Southwest and High Plains.

...Guidance/Predictability Assessment...

Medium-range guidance clustering continues to improve with the
latest several run cycles to bolster forecast confidence.
Lingering shortwave and local convective rainfall focus variances
tend to be mitigated with a guidance composite forecast approach.
Favor a transition from a composite model blend Tuesday-Thursday
to a broader model/ensemble mean/machine learning blend later next
week given some uncertainty growth. This plan acts to maintain
good WPC product continuity and threat messaging that remains
overall reasonably well in line with the National Blend of Models.

...Weather/Hazards Highlights...

It generally remains the case that strong upper ridge remaining
positioned over the southern U.S. will maintain hot conditions
across the southern Plains through the Lower Mississippi Valley,
Tennessee Valley, and Southeast. Afternoon temperatures will
commonly reach the upper 90s to lower 100s across the interior
South, while high humidity and persistent elevated dewpoints will
produce oppressive heat indices of 105-115 degrees. Record-breaking
warm overnight temperatures will further limit recovery,
particularly where several consecutive days of heat occur.
Widespread Major to Extreme HeatRisk conditions should persist into
much of next week and also gradually spread over the Southwest
U.S..
Several consecutive days of high heat stress can lead to heat-
related illnesses. See WPC's Key Messages for more information.

Shortwave energy moving through the northern tier will carry
frontal systems that could focus moisture for rounds of showers and
thunderstorms next week. After some rain in the northern
Rockies/Plains to Upper Midwest Monday, stronger energy and a cold
front are forecast to bring increasing rain amounts to the Upper
Midwest in particular by Tuesday. A Slight Risk remains in place
in the Day 5/Tuesday Excessive Rainfall Outlook for afternoon and
overnight strong to severe thunderstorm and MCS activity. Enhanced
rainfall could continue into the Great Lakes region Wednesday,
with some rain chances starting to spread into the Northeast as
well. Farther south, a weak cold front or two should provide a
focus for scattered thunderstorms in the Mid- South to southern
Mid-Atlantic on Monday and across the Southeast Tuesday- Wednesday
in the hot and unstable airmass. By Thursday this activity may all
combine into chances for scattered showers/storms across the
Eastern Seaboard. Meanwhile, some monsoonal moisture could bring
scattered diurnally driven convection to the Southwest. Monsoon
coverage should likely be less than during the short range period,
with less support aloft as the upper ridge builds. But some
moisture advecting north while additional energy rounds the north
side of the upper ridge could lead to more rounds of rain/storms in
the north-central U.S. later next week.


Tate/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