Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
320 AM EDT Fri Aug 14 2026

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


...Long-duration heat wave continues in the Southeast...

...Heavy rain threat gets renewed in Midwest by Tuesday...


...Overview...

Southern tier upper ridging will be well established into next week
and bring continued 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 northern tier.
Rainfall amounts are forecast to peak in the Midwest Tuesday and
the Great Lakes Wednesday, with some flash flooding threat.
Additionally, some monsoonal moisture coming north under the ridge
will allow for convection in the Southwest and High Plains.


...Guidance/Predictability Assessment...

Model guidance remains quite agreeable regarding the broad upper
ridge stretching across the southern tier early next week. As the
week progresses, troughing across the northeastern quadrant of the
U.S. could sink south and limit the upper high to the southwestern
U.S.

Farther west, there have been considerable model differences with
the potential for energy to come into the Northwest. Through its
18Z run, the GFS had been persistent in showing an aggressive
shortwave digging through the Northwest by Tuesday-Wednesday
forming a closed low, out of phase with basically any other
guidance. Fortunately, the new 00Z GFS has backed off and now shows
a shallower shortwave more like the other dynamical and AI models.
There remain some model differences with the evolution of this and
other shortwaves, but more within typical spread for the medium
range period. Namely, the 00Z GFS is a little deeper and slower
with the shortwave in the central Plains by Thursday, while the 00Z
ECMWF is on the aggressive side with the strength of a surface low
moving through the Great Lakes region Wednesday eastward.

For late week, troughing looks to march east through the Pacific
toward North America, potentially from both the midlatitudes and
the Northeast Pacific. 00Z model guidance has converged somewhat on
the timing of this troughing, though minor differences remain. The
ridging just downstream across the West may extend northward in
response.

The WPC forecast was based on a multi-model blend not favoring the
older GFS runs, though the 00Z GFS seems reasonable enough to
include in a blend. As the period progressed, increased the
proportion of ensemble means to about half by Day 7 amid the
increasing spread.


...Weather/Hazards Highlights...

The 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. 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 is in place in the
Day 5/Tuesday Excessive Rainfall Outlook for this 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 warm 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


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