Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
303 PM 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...

Heatwave to persist across portions of the southern tier this
weekend and into the coming week thanks to a persistent upper high.
The longest period of hazardous heat will be 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. Meanwhile, multiple shortwaves should maintain troughing in
the East, leading to rain and thunderstorms across the Eastern
Seaboard into the weekend.


...Guidance/Predictability Assessment...

The latest suite of guidance has decent agreement with the large
scale pattern with the anchoring upper high and troughing in the
East. Multiple shortwaves will be passing through the trough
during the extended period which brings uncertainty to its depth
and evolution. The last few model cycles have shown the GFS
solution diverging from the cluster by taking progressing the
closed low faster and to the north; the majority/AI solutions favor
a position near the Great Lakes/Canada through Monday.

Meanwhile, a shortwave trough will be moving inland across the
Pacific Northwest Saturday however timing differences increase
thereafter. GFS continues to be 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.

Another trough/low is anticipated to track from the northeast
Pacific toward the Pacific Northeast Coast by midweek. In general
guidance is onboard with this however the CMC depicts a notably
more progressive 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.

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 will be possible,
particularly 
for 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.


Campbell/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