879
FXUS02 KWBC 201957
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
357 PM EDT Thu Aug 20 2026

Valid 12Z Sun Aug 23 2026 - 12Z Thu Aug 27 2026


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


...Overview...
A strong and persistent upper high will maintain hazardous heat
across the southern tier through next week, particularly across the
Southern Plains and Lower Mississippi Valley. Monsoonal moisture
is forecast to stream north under the ridge for scattered
convection across the Intermountain West and Rockies, while rounds
of rain dive through portions of the central U.S. as well.
Meanwhile, multiple shortwaves should maintain troughing in the
East. Rain is likely for the Northeast early next week as the
first low pulls away, and then rain and thunderstorms are forecast
to overspread parts of the eastern U.S. again Tuesday and
Wednesday.


...Guidance/Predictability Assessment...
Forecast guidance depicts a fairly stagnant synoptic pattern
characterized by a strong upper-high anchored in the Southwest,
and troughing in the East. Dynamical/AI models show relatively
good agreement with a closed upper low center near the Great Lakes
and adjacent Canada Sunday-Monday, with some lingering surface low
position differences. Upstream, a potent shortwave will round the
northern side of the ridge, tracking across southern Canada
Monday/Tuesday. Despite shortwave differences with how the wave
evolves beyond Tuesday, there is a general consensus for this
feature to reinforce the troughing pattern over the East for Days
6-7.

Meanwhile, a trough/low is forecast to dive from the northeastern
Pacific and track near the Pacific Northwest by midweek. 12Z model
guidance has shown better clustering with the timing of this
system, although the GFS is still on the fast end of the envelope,
in contrast to the ECMWF (now the middle ground solution) and EC-
AIFS (now slower and more wound-up). As such, the latest WPC
forecast maintained a multi-model blend of dynamical and AI
guidance early in the forecast period, while transitioning towards
the ensemble means with time.


...Weather/Hazards Highlights...

Hot temperatures well into the 100s, with oppressive heat indices,
are forecast across the south-central U.S. into 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. Farther west,
highs near and above 110 in the Desert Southwest could also cause
heat concerns next week. Areas of the Southeast may reach a few
degrees above normal at times with moist dewpoints. See WPC`s Key
Messages for more on the extreme heat. Elsewhere, most areas will
be close to average for temperatures, with the Ohio Valley and
vicinity a bit below average early in the week under upper
troughing.

An upper/surface low in southeast Canada pulling away will bring
rain chances to the Northeast on Sunday, potentially lasting across
the interior Northeast for Monday-Tuesday. Through the period,
monsoonal moisture is forecast to bring scattered, diurnally driven
showers and thunderstorms to the Intermountain West/Rockies.
Isolated flash flooding is possible especially across sensitive
areas like burn scars, favored terrain like slot canyons, and urban
areas. 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 rainfall
positions and amounts are uncertain, but generally the
Northern/Central Plains and the Mississippi Valley could be
impacted early in the week. Rain chances are forecast to push into
the Midwest/Great Lakes and Southeast Tuesday and could overspread
much of the Eastern Seaboard by midweek.


Asherman/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




$$