644
FXUS02 KWBC 091945
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
345 PM EDT Sun Aug 9 2026

Valid 12Z Wed Aug 12 2026 - 12Z Sun Aug 16 2026


...Multi-day heavy rainfall threat extending from parts of the
Midwest to the Ohio Valley this week...

...Hazardous heat forecast across much of the South-Central and
Southeast U.S. through next weekend...


...Overview...

A progressive and unsettled regime across the northern and eastern
U.S. and ridging over south-central U.S. will continue through at
least early next weekend. The upper ridge will bring hazardous
heat across the Southeast and southern Plains through Saturday. The
shortwave embedded in the amplified flow will support
thunderstorms and showers across the Northern Tier. Multiple days
of slow-moving storms across portions of the Midwest and Ohio
Valley may lead to flooding concerns. Troughing over the West
Coast/Pacific Northwest will reinforce showers and thunderstorms
activity stretching across the Southwest and Intermountain
West/Great Basin.


...Guidance/Predictability Assessment...

The large-scale pattern is reasonably well established through the
first half of the period, with good agreement among the latest
deterministic and ensemble guidance on the persistence of an
active northern- tier flow and ridging over the south-central U.S.
Confidence decreases with time concerning the amplitude and exact
placement of shortwave troughs crossing the northern CONUS, which
will impact the placement of frontal boundaries and areas of heavy
rainfall. For the forecast, a preference towards a multi-model
blend for the first portion of the period was used, while
incorporating a heavier weight on the ensemble means by day 6.


...Weather/Hazards Highlights...

Across the northern tier a series of shortwave energies will eject
eastward into the broad troughing over eastern U.S. through the
period. This will promote unsettled weather as the associated slow
moving frontal boundary drapes across portions of the
Rockies/Plains into the Great Lakes/Ohio Valley and across the
Northeast. The warm and moist air mass ahead of these disturbances
will support sufficient instability and lift for organized
clusters, especially over the Midwest, Ohio Valley, and parts of
the Mid- Atlantic. High rain rates from the slow moving and
possibly repeating storms may lead to flash flooding concerns,
which is highlighted in the Day 4 and 5 (Wednesday and Thursday)
Excessive Rainfall Outlooks (ERO). The ERO shows a broad Marginal
Risk across the northern/central Plains/Rockies into the Mid-
Mississippi Valley, Ohio Valley/Tennessee Valley, and portions of
the Southeast, with a Slight Risk over portions of the Ohio
Valley/Central Appalachians (for Wednesday/Day 4) and Midwest to
the Ohio Valley (for Thursday/Day 5).

For the remainder of the week into the weekend, the surface low
and associated stationary front will linger over the High Plains
and central U.S. As sufficient moisture accumulates along the
boundary and instability increases, daily thunderstorm chances will
continue. With the potential for organized convection to develop
as shortwaves energy, the flash flooding concerns may continue.
Additional shower/thunderstorm chances will round the south-central
U.S. ridge and bring rainfall chances to more of the Northern
Plains and Southeast.

Across the Southwest and throughout much of the Intermountain West
and Rockies, an active convective pattern continues as the ridging
weakens by midweek and monsoonal moisture continues to produce
thunderstorms through the week. With chances for multiple days of
repeated showers and thunderstorms, flash flooding concerns will
increase across portions of the Southwest, Rockies, interior
California, and Great Basin, especially over burn scars, urban
areas, slot canyons, and steep terrain.

The ridge over southwest will move eastward through the week and
restrengthen over the Mid-South by next weekend, bringing
hazardous heat across the Southeast, Gulf Coast, and portions of
the Southern Plains. With high humidity from the Gulf, heat indices
may become oppressive as widespread Major HeatRisk with locally
Extreme HeatRisk levels spreads across much of the area. Portions
of the southern Plains will see highs in the low 100s, while the
Southeast will see mid to upper 90s. Heat- related impacts could
become significant where the combination of high temperatures and
humidity persist for several consecutive days.


Oudit/Snell



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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