165
FXUS02 KWBC 121838
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
238 PM EDT Wed Aug 12 2026

Valid 12Z Sat Aug 15 2026 - 12Z Wed Aug 19 2026


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

...Heavy Rain Threats for the Rockies, Central Plains, Midwest,
and Mid-Atlantic through this weekend...


...Overview...

An expansive upper ridge over the Southeast will continue to build
west through the middle of next week across the southern tier of
the Lower 48, bringing a prolonged period of hazardous heat across
the south-central U.S. and Southeast. The jet stream pattern will
continue to support rounds of showers and thunderstorms that
stretch from areas as far south and west as Arizona and New Mexico
to as far north and east as the Northeast. Repeated rounds of heavy
thunderstorms may cause areas of flooding. Heavy rain will also be
possible with daily monsoonal thunderstorms from the Southwest
into the southern Rockies.


...Guidance/Predictability Assessment...

The latest guidance remain in fairly good agreement on the larger-
scale pattern through this weekend. Model spread begins to increase
early next week with the evolution of a deepening trough west of
California. Some guidance is slower to eject the developing trough
while others are faster. Generally, deepening troughs that become
cut-off from the mean flow tend to move more slowly than modeled,
so leaned more on the slower end of guidance for the 500mb
forecast in the West. Confidence remains higher in the ridge-axis
positioned across the southern tier and periodic shortwave
disturbances within the zonal flow across the northern states,
while confidence is lower on the timing and magnitude of individual
surface waves and their associated precipitation maxima.


...Weather/Hazards Highlights...


The upper ridge across the southern U.S. will be responsible for
widespread, well above normal temperatures from the South-Central
U.S. to the Southeast. Portions of the Southern Plains and Lower
Mississippi Valley will reach the lower 100s, while widespread 90s
extend eastward across the Southeast this weekend. Parts of the
Southeast will see daytime highs reach the century mark by Monday.
Searing high temperatures coupled with elevated dew points will
allow for dangerous heat conditions each day. Record warm overnight
temperatures will provide little relief as well, exacerbating the
effects of the heat wave. Widespread Major to Extreme HeatRisk
conditions are expected across these regions. Several consecutive
days of high heat stress can lead to heat-related illnesses.

Meanwhile, monsoonal moisture over the Southwest will be carried
northward through the Central Plains this weekend. Widespread
showers and thunderstorms will remain in the forecast across
Arizona, New Mexico, and northward into the central Rockies and
High Plains given their ideal placement on the western periphery of
the upper-level ridge. WPC maintains a Marginal Risk (threat level
1/4) from the Rio Grade River on north through the Central Plains,
including a Day 4 Slight Risk (threat level 2/4) in northeast
Colorado and central Nebraska. The Day 5 ERO maintains a Marginal
Risk in similar areas, highlighting the potential for additional
heavy rainfall through Sunday.

The same influx of anomalous moisture over the Southwest will be
directed into the Midwest late week. This pool of anomalous
moisture spills east into the Ohio Valley and Great Lakes by
Saturday, then finally into the Northeast and Mid-Atlantic by
Sunday. As shortwave disturbances and nearby frontal boundaries
embedded within the zonal flow pattern pass over the northern U.S.,
they will generate widespread showers and thunderstorms.
Additionally, some areas containing saturated/sensitive soils could
see instances of training thunderstorms as well, raising the
potential for flash flooding. This is most concerning over portions
of the Upper Midwest where a Slight Risk for the Day 4/Saturday
ERO is in place, while a broad Marginal Risk highlights parts of
the Midwest and Great Lakes. By Sunday, the focus for organized
thunderstorms and heavy rainfall shifts towards portions of the
Great Lakes, Ohio Valley, northern Mid-Atlantic, and Northeast as
the frontal system advances eastward. This is highlighted by a
Marginal Risk over parts of these regions on the Day 5/Sunday ERO.
By Monday, a frontal boundary positioned west-to-east from the
Central Plains to the Mid-Atlantic will be the focus for additional
showers and storms. Showers and storms will be possible in the
Southeast on Tuesday as the front sinks southward, while another
upper-level disturbances delivers more thunderstorms across the
northern High Plains and Upper Midwest.


Mullinax/Oudit



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






$$