350
FXUS02 KWBC 080537
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
137 AM EDT Sat Aug 8 2026

Valid 12Z Tue Aug 11 2026 - 12Z Sat Aug 15 2026


...Overview...

Upper troughing and shortwave disturbances will bring thunderstorms
and showers across north-central and eastern U.S. through late
week. Multiple days of heavy rainfall may lead to localized
flooding concerns. The ridge will move eastward, bringing above
normal temperatures across southern Plains into Southeast.
Southerly flow will continue to funnel monsoonal moisture across
the Southwest/Southern CA, leading to daily thunderstorm
development.


...Guidance/Predictability Assessment...

Latest deterministic and ensemble guidance generally agrees on the
large-scale evolution, although uncertainty remains regarding the
amplitude and timing of individual shortwave impulses embedded
within the northern-stream flow. Model spread increases towards the
latter portion of the period, especially with frontal placements.
This will impact the confidence in the location for the greatest
heavy rainfall threat. However, the broader signal for
precipitation potential across parts of the Upper Midwest into the
Great Lakes and Northeast is reasonably well supported. CMC seemed
to be a outlier in some of the smaller-scale features compared to
the GFS/ECMWF. Therefore, a model blend of ECMWF/GFS weight in the
forecast were heavier than the CMC, while gradually phasing in the
ensemble means towards day 5.


...Weather/Hazards Highlights...


The increasing troughing over northern/eastern U.S. will bring
thunderstorm and showers development, especially over areas where
deep moisture, instability, and slow- moving boundaries overlap.
Additionally, the shortwave crossing the northern Rockies/High
Plains will move towards the Great Lakes/Upper Midwest. A surface
low and trailing frontal boundary will accompany this feature as it
interacts with moist and unstable airmass, leading to thunderstorm
development along the front. With the slow- moving, organized
convection, locally heavy rainfall will be possible across the
Great Lakes/Midwest into the Ohio Valley and portions of the Mid-
Atlantic, as well as portions of the northern/central Plains
through Wednesday. Across the Southeast, abundance low-level
moisture will maintain a risk of thunderstorms that can lead to
localized flooding where repeated storms may develop.

The frontal boundary will stall and drape across the central
Plains into the Ohio Valley and Northeast by late-week, reinforcing
another round of thunderstorms and showers through Friday. High
rainfall rates and repeated rounds of convection can lead to
localized flooding concerns along the boundary.

Over into southwestern U.S., the persistent ridging will start to
move eastward, but monsoonal moisture will continue to generate
thunderstorms over the Southwest. Multiple days of showers and
thunderstorms may lead to locally heavy rainfall and flash flooding
across the Southwest and parts of Southern CA, particularly over
burn scars and steep terrain. The ridge will support hazardous heat
building over the southern Plains, Southeast and Gulf Coast by
midweek. Heat- related impacts could become significant where the
combination of high temperatures and humidity persist for several
consecutive days.



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






$$