866
FXUS02 KWBC 131856
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
256 PM EDT Wed Aug 13 2025

Valid 12Z Sat Aug 16 2025 - 12Z Wed Aug 20 2025

...Overview...

Troughing initially over the Northeast Pacific and CONUS West
Coast will slowly retrograde westward as an upper high over the
Lower Mississippi Valley moves westward to the Four Corners
region. A fairly active, wet pattern focused over the north-
central states will shift southeast to Great Lakes region this
weekend and to the Mid-Atlantic region by midweek thanks to upper
level jet stream. Rainfall is also expected for the Southeast and
Southwest. Much of the Midwest and East will begin with very warm
temperatures for mid August and the heat will spread westward as
the week progresses.


...Guidance/Predictability Assessment...

The latest guidance continues to be fairly clustered with an upper
low offshore the Pacific Northwest/British Columbia coast and a
broad ridge over much of CONUS and southern Canada. A consensus
approach for the fronts/pressures and sensible weather provided a
good starting point and included the GEFS and EC ensemble means
toward the later periods to help smooth out some of the spread,
particularly for the Eastern Seaboard/offshore. The National
Hurricane Center is tracking Tropical Storm Erin, which may skirt
the eastern part of the domain next week per the latest forecast.
Please see the NHC website for the most up-to- date information.


...Weather/Hazards Highlights...

There will be three main regions where excessive rainfall and
isolated areas of flash flooding may develop for this weekend --
the Upper Midwest, Southeast/northern Florida, and the Southwest.
A continuous surge of moisture into the Southwest combined with
diurnal heating may trigger storms capable of producing heavier
rainfall that may fall over more sensitive areas (steep terrain,
in/around burn scars, etc.). The footprint for rainfall potential
will shift eastward with time. Over the northern region, a wavy
frontal boundary will act as a focus for showers and thunderstorms
with locally heavy rainfall. The exact placement of the heaviest
QPF remains a bit uncertain however there are models signals for multi-
inch amounts. For the Southeast, persistently high moisture levels
when combined with afternoon heating, will trigger showers and
storms development both days as the remnant moisture of an old
front continue to sag southward.

A vast portion of the central and eastern U.S. will remain above
normal for daily maximum temperatures this weekend, with with many
areas climbing into the 90s (heat indices around 100F). This will
drive HeatRisk values into the the Moderate (level 2) to Major
(level 3 out of 4) category from the Corn Belt through the Midwest
into the Mid- Atlantic. High temperatures married with high
dewpoints across the Lower Mississippi Valley and Florida will keep
conditions muggy and unpleasant into next week. Portions of the the
Great Lakes and Northeast will start to get relief from the heat as
cooler air filters in with an advancing cold front. Across the
West cooler than mid-August values to start will moderate as the
troughing eases back westward. Above normal temperatures will
likely return to the Four Corners region by Tuesday as the upper
ridge moves into the area from the east. This may bring more
widespread Moderate HeatRisk values to the region with temperatures
back to around 110F in the lower deserts.

Campbell

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 (QPF), excessive rainfall
outlook (ERO), winter weather outlook (WWO) probabilities, heat
indices, and Key Messages can be accessed from:

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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