837
FXUS02 KWBC 261956
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
356 PM EDT Wed Aug 26 2026

Valid 12Z Sat Aug 29 2026 - 12Z Wed Sep 02 2026


...Hazardous Heat from the Desert Southwest and Texas to
reposition across the South-Central U.S. and Mid-South...


...Overview...

Dangerous late-summer heat across the Desert Southwest and Texas
will spread northward across the central/southern Plains and Mid-
South this weekend into next week. Surges of monsoonal moisture
will support daily showers and thunderstorms over portions of the
Southwest and Intermountain West/Rockies with localized flash
flooding possible. Meanwhile, a couple of low pressure systems
traversing southern and western Canada will push a wavy front
across the northern tier of the CONUS, and later dip into the
east-central U.S. where rounds of showers and possibly strong to
severe thunderstorms with locally heavy downpours are possible.
Slowly dissipating frontal boundaries across the southern Mid-
Atlantic and Southeast will offer lingering risks for storms with
heavy rain and local runoff issues.


...Guidance/Predictability Assessment...

Guidance remains in overall good agreement on the synoptic weather
pattern, though uncertainty with the timing of systems working
through the Northwest to the U.S. northern tier remains. Models
this morning show general agreement with the ECMWF on a slower
eastward ejection of the wave/low-pressure system across southern
Canada early to middle of next week. In response to the slower wave
ejection, there is a notable northeastward expansion of the
southern U.S. upper ridge toward the lower Great Lakes and the Ohio
Valley early next week, implying a possibility for the heat to
expand further north into the Midwest, Ohio Valley, lower Great
Lakes, and possibly downstream into the Mid-Atlantic by midweek.

Nevertheless, given general larger-scale agreement, favor a
general consensus of the deterministic and ensemble means from the
00Z ECMWF/EC mean, 06Z GFS/GEFS, and the 00Z CMC/CMC mean over
time that seems to provide a good general forecast and threat
messaging baseline in line with continuity. The blend process tends
to mute/mitigate embedded smaller scale system differences as
consistent with individual predictability, but maintains main
focusing features. The most notable change from the previous
forecast cycle was a slower eastward progression of the low-
pressure system across southern Canada.


...Weather/Hazards Highlights...

Under the influence of the upper high/ridge this week, daily
maximum temperatures across the southern Plains will continue to
rise into the 90s and 100s with oppressive heat indices. Record-
breaking warm overnight temperatures across the southern tier will
further limit recovery from the heat, resulting in widespread Major
to Extreme HeatRisk that may cause heat related illnesses. As the
upper ridge flattens into this weekend and shifts eastward into
early-mid next week, hazardous heat will refocus over the southern
Plains and steadily expand north across the south-central U.S and
lower to mid-Mississippi Valley/Mid-South with some triple digit
maximum temperatures and more widespread record hot overnight
values. In this upper pattern transition, expect excessive heat
threat moderation over the Desert Southwest this weekend into next
week. Please see WPC`s Key Messages for more extreme heat details.

Monsoonal moisture streaming northward on the western to northern
periphery of the upper ridge and ahead of locally showery Northwest
U.S. upper troughing will continue to fuel scattered, diurnally
driven convection from the Southwest and Intermountain West to the
Rockies. Individual cells may lead to isolated instances of flash
flooding for sensitive locations such as burn scars, favored
terrain like slot canyons, and urban areas. Marginal Risk areas
cover portions of these broad areas on the WPC Day 4/Saturday and
Day 5/Sunday Excessive Rainfall Outlooks (EROs).

Shortwaves rounding the top of the ridge and pivoting into the
downstream mean upper trough while interacting with wavy frontal
systems will bring much of heavy rain and thunderstorms further off
the East Coast this weekend into next week. Weekend Marginal Risk
ERO areas spotlight a focus over the upper Midwest ahead of the
triple-point associated with the eastward-moving low-pressure
system across southern Canada. Meanwhile downstream, weekend
Marginal Risk ERO areas highlight a protracted threat for rounds
of locally heavy rainfall over the southern Mid-Atlantic and the
coastal Southeast on Saturday, confining to the central and eastern
Gulf Coast into western Florida by Sunday as wavy front gradually
dissipates.


Kong/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





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