Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
333 AM EDT Wed Aug 19 2026

Valid 12Z Sat Aug 22 2026 - 12Z Wed Aug 26 2026


...Hazardous heat will continue across the southern Plains and
Lower Mississippi Valley...


...Overview...

A strong and persistent upper high will be in place over the Four
Corners states to southern/central Plains this weekend into next
week, maintaining hazardous heat that will last the longest across
the southern Plains and Lower Mississippi Valley. Monsoonal
moisture is forecast to stream north under the ridge for scattered
convection across the West, while rounds of rain dive through
portions of the central U.S. as well. Meanwhile, multiple
shortwaves should maintain troughing in the East, leading to rain
and thunderstorms across the Eastern Seaboard into the weekend.


...Guidance/Predictability Assessment...

Model guidance remains agreeable on a fairly stagnant pattern,
with the anchoring upper high and troughing in the East. The
multiple shortwaves within the trough and its evolution/depth from
day to day are less certain. Most dynamical/AI models are showing
relatively good agreement with a closed upper low center near the
Great Lakes and adjacent Canada Sunday-Monday, though the GFS
(including the new 00Z run) is farther north and more progressive.

Upstream, AI and dynamical model guidance agree on a shortwave
moving from the eastern Pacific into the Northwest Saturday, but
timing differences remain a challenge. GFS runs including the 00Z
as still a bit faster than consensus as the shortwave moves quickly
across southern Canada Sunday-Monday and toward the Upper Midwest
Tuesday. This shortwave could serve to deepen the trough in the
East again by midweek as it dives into the Midwest/Great Lakes,
after the trough becomes shallower Monday-Tuesday. The 00Z GFS even
creates a closed low over the Upper Great Lakes from this feature,
which seems possible, but it is stronger than other models.

Then a trough/low is forecast to dive from the northeastern
Pacific nearing the Pacific Northwest for midweek. Models are
agreeable with this, except for the CMC (12Z and 00Z), which shows
a much faster track across Canada and the U.S. northern tier than
consensus, becoming out of phase with central North American
troughing where other models have ridging by Wednesday.

Thus, the WPC forecast used a multi-model blend early in the
period, and then leaned away from the GFS and CMC in favor of the
ECMWF, AIFS/AIGFS, and increasing proportions of the ensemble
means.


...Weather/Hazards Highlights...

Hot temperatures well into the 100s, with oppressive heat indices,
are forecast across the south-central U.S. for the weekend and
into much of next week under the strong upper high. Record-breaking
warm overnight temperatures across the southern tier will further
limit recovery from the heat, especially since several consecutive
days of heat will occur. Widespread Major to Extreme HeatRisk will
persist in the southern Plains and Lower Mississippi Valley.
Several consecutive days of high heat stress can lead to heat-
related illnesses. The West should also see warm to hot
temperatures primarily Saturday when the upper ridge reaches the
farthest north. The Southeast should see some minor relief over the
weekend as the trough aloft and weak cold fronts lessen the
magnitude and scope of the heat, but could gradually warm again as
next week progresses.

Over the weekend, combining energies and frontal systems will
allow for widespread rain and thunderstorms across the East. Rain
amounts should generally stay light to moderate, but some heavier
amounts are possible in coastal areas of the Mid-Atlantic Saturday,
with isolated flash flooding possible. By Sunday rain chances are
forecast to focus in the Great Lakes/Appalachians/Northeast as the
surface low/frontal systems move through, and some could linger
Monday for the Interior Northeast on the backside of the low.
Scattered showers and thunderstorms remain possible for Florida
through the period.

Monsoonal moisture is forecast to bring scattered, diurnally
driven showers and thunderstorms to the Intermountain West through
the period. Localized flash flooding is possible especially across
sensitive areas like burn scars, favored terrain like slot canyons,
and urban areas. A round of rain is also possible with a shortwave
in the Pacific Northwest and into the northern Rockies, likely
peaking Saturday. Areas of rain and storms are also possible in the
central U.S. as shortwaves round the northeast side of the ridge
and dive southeast. Placement of these shortwaves and thus the rain
chances are uncertain, but generally the northern/central Plains
and the Mississippi Valley could be impacted, reaching the
Southeast into the workweek.


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