214
FXUS02 KWBC 111913
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
313 PM EDT Tue Aug 11 2026

Valid 12Z Fri Aug 14 2026 - 12Z Tue Aug 18 2026


...Hazardous Heat in the South-Central and Southeast U.S...

...Heavy Rain Threats for the Southwest, Rockies, Midwest, and
Mid-Atlantic...


...Overview...

An expansive ridge of high pressure will build across the southern
U.S., bringing a prolonged period of hazardous heat to the South-
Central U.S. and Southeast. Meanwhile, upper level energy moving
across southern Canada will trigger cyclogenesis over the northern
Plains. This system will track across the Midwest and Mid-
Atlantic, accompanied by a heavy rain threat. Heavy rain will also
be possible with daily monsoonal thunderstorms from the Southwest
into the Great Basin and southern Rockies.


...Guidance/Predictability Assessment...

Model guidance is in good agreement on the synoptic scale weather
pattern, leading to a fairly high confidence forecast. There is
some timing uncertainty with energy embedded in the mainly zonal
flow across southern Canada, which may affect precipitation timing
and amounts from the Midwest to the Mid-Atlantic. Even so, high
precipitable water content up through the Midwest should still
support a heavy rain threat. Uncertainty also surrounds a cutoff
low moving south in the eastern Pacific. There is a large spread in
the location of this feature, but this system has few sensible
weather impacts to the U.S. at this time.

The WPC forecast was initiated using a near even blend of the
available deterministic models through the weekend, with increasing
contributions from ensemble means through early next week. This
maintained consistency with the previous forecast.


...Weather/Hazards Highlights...

A prolonged heat wave will linger from the South-Central to
Southeast U.S. under the influence of a persistent upper ridge.
Temperatures will remain well above normal as portions of the
southern Plains and Lower Mississippi Valley reach the lower 100s,
while widespread 90s extend eastward across the Southeast. High
dew points/humidity will keep heat indices elevated, resulting in
dangerous heat conditions, and record warm overnight temperatures
will provide little relief. Widespread Major to Extreme HeatRisk
conditions are expected across these regions.

Meanwhile, monsoonal moisture and flow embedded vorts will channel
over the Southwest, Great Basin, and southern Rockies between an
eastern Pacific upper trough and the western periphery of the
southern U.S. upper ridge this period. This will lead to daily
rounds of scattered to numerous thunderstorms, particularly over
the southern Rockies where the Day 4/Friday Excessive Rainfall
Outlook (ERO) depicts a Slight Risk area. The Day 4/Friday and Day
5/Saturday EROs also show broad surrounding Marginal Risk areas
that encompass areas from the Southwest to the Great Plains. Some
storms will produce excessive rainfall over short periods while
moving rather slowly. Repeated convection may lead to flash
flooding in vulnerable terrain, including burn scars, slot canyons,
and urbanized areas.

Across the northern tier, waves of energy embedded in the progressive
flow will interact with a developing low pressure/frontal system
over the Midwest this weekend. Rich low-level moisture,
instability, and forcing will support periodic clusters of showers
and strong thunderstorms with locally heavy rainfall potential and
flooding concerns. The Day 4/Friday ERO has introduced a Slight
Risk threat area centered over the corn belt given repeat
convection potential. The Day 4/Friday and Day 5/Saturday EROs also
show broad surrounding Marginal Risk areas extending across the
Midwest and Great Lakes. The heavy rainfall threat is expected to
expand into the Mid-Atlantic and Northeast as the system
progresses early next week.


Dolan/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


$$