225
FXUS02 KWNH 210708
PREEPD

Preliminary Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
307 AM EDT Fri Aug 21 2026

Valid 12Z Mon Aug 24 2026 - 12Z Fri Aug 28 2026


...Hazardous heat to continue from the Lower Mississippi Valley
and Southern Plains to the Desert Southwest...


...Overview and Guidance/Predictability Assessment...

A favored composite of reasonably well clustered model, ensemble
mean and machine learning guidance depicts a stagnant upper pattern
next week as highlighted by a strong upper-high anchored over the
Southwest and east-central U.S. mean troughing.

Hazardous heat across much of the U.S. southern tier may persist
for the rest of August, particularly across the Southern Plains
and Lower Mississippi Valley. Monsoonal moisture will stream north
around the ridge to fuel scattered Intermountain West and Rockies
convection as strong convection with local downpours spill across
parts of the central U.S.. Shortwaves will maintain upper troughing
over the east-central U.S. to favor wavy and moderating frontal
surges. Wrapping rains likely for the Northeast early next week as
a lead low pulls away will be followed by periodic bouts of
rain/thunderstorms for portions of the East Tuesday-Friday.

...Weather/Hazards Highlights...

Hot temperatures well into the 100s, with oppressive heat indices,
are forecast for the south-central U.S. through next week under
the strong upper high. Record-breaking warm overnight temperatures
across the southern tier will further limit recovery from the heat,
especially given heatwave longevity. 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. Please see WPC`s Key Messages for more
on the extreme heat. Elsewhere, most areas will see near average
temperatures, with the Ohio Valley and vicinity below average.

A slowly exiting low will keep wrapping rain chances for the
interior Northeast early next week. Through this 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. WPC
Excessive Rainfall Outlook (ERO) Marginal Risk areas are in place
there. Areas of rain and strong to severe 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 offer uncertainty over the
central/east U.S., but frontal proximity and a pooling
moisture/instability focus over the central Plains prompted
introduction of an ERO Marginal Risk area to further monitor given
cell training threat. Rain chances working to the Midwest/Great
Lakes and Southeast Tuesday may periodically develop and also
overspread much of the Eastern Seaboard over mid-later next week.


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






$$