844
FXUS02 KWBC 290602
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
202 AM EDT Sat Aug 29 2026

Valid 12Z Tue Sep 01 2026 - 12Z Sat Sep 05 2026


...Dangerous heat will expand from the central and southern Plains
to the Mid-Atlantic and Southeast next week...

...Pattern Overview...

Extreme late summer heat will spread across the south-central and
southeastern U.S. next week, increasing the likelihood of heat
related illnesses. Monsoonal moisture will continue to support
numerous showers and thunderstorms across portions of the Southwest
and the Intermountain West/Rockies with localized flash flooding
possible. Farther north, a strong Pacific storm coupled with a
potential atmospheric river will bring notable rainfall to parts of
the Pacific Northwest. Downstream, heavy rainfall and severe
weather will be possible from the northern Plains and the Upper
Midwest to the Great Lakes and Northeast.


...Guidance/Predictability Assessment...

The latest available model guidance has a fairly good handle on
the overall large scale pattern through most of the medium range
period. The dominant features include persistent upper troughing
across the Pacific Northwest, a potent shortwave/closed low
tracking eastward across southern Canada (which leads to troughing
over the Eastern U.S.) and a sprawling upper ridge mostly centered
from the central/southern Plains to the Southeast. There are still
some timing and amplitude differences of smaller scale disturbances
ejecting out of the Southwest and riding over top of the ridge,
which will have downstream impacts to possible heavy rain and
severe weather threats across the Northeast mid to late week. To
mitigate these differences while preserving the large scale
footprint, a multi-model blended approach was utilized. The blend
favored the deterministic solutions of the GFS, EC, EC-AIFS, and
CMC early on in the period, before transitioning heavier weighting
to the EC ensemble mean later on.


...Weather/Hazards Highlights...

An intense and dangerous late summer heat wave will spread from
the central and southern Plains to the Midwest, Mid-Atlantic, and
Southeast next week as a large and sprawling upper level ridge
dominates the region. High temperatures climbing well into the 90s
and 100s combined with high humidity and very warm overnight lows
in the 70s to near 80 will result in widespread areas of Major to
Extreme HeatRisk. Please see WPC`s Key Messages for more details.

Monsoonal moisture streaming out ahead of persistent Pacific
Northwest upper troughing and Central/Eastern U.S. upper ridging
will continue to spark numerous showers and thunderstorms across
portions of the Southwest, Intermountain West, and Rockies each
afternoon and evening through most of next week. Given the
anomalous moisture in place, many thunderstorms are likely to
produce heavy rainfall. Any slower-moving downpours may lead to
isolated instances of flash flooding, especially for more
vulnerable areas like burn scars, slot canyons, and urban areas.

Persistent troughing and a strong Pacific storm coupled with a
potential atmospheric river will likely result in a multi-day heavy
rainfall event across parts of the Pacific Northwest beginning
late Tuesday night and lasting through Wednesday and possibly
Thursday. The heaviest rain will mostly fall on Wednesday and be
confined to coastal areas of Washington and Oregon, along with the
Cascades. The rainy, cloudy, and generally unsettled weather will
keep temperatures on the cooler side of normal for most of next
week.

Farther downstream, a series of dynamic shortwaves and frontal
systems tracking eastward along the northern periphery of the
elongated upper ridge will interact with high humidity and
instability to produce a few episodes of heavy rainfall and
possible severe weather from the northern Plains, Upper Midwest,
Great Lakes, and Northeast Tuesday into Wednesday. Given the
increasing signal for notable rainfall across portions of the
Interior Northeast and New England on Wednesday, localized to
scattered instances of flash flooding would be possible and
forecasts will need to be monitored over the next few days.


Miller


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


$$