965
FXUS02 KWNH 130644
PREEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
243 AM 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. Across the Northern Tier, the jet stream will maintain a
fairly active weather pattern this weekend into the start of the
week before it shifts a bit farther southeast. The very warm
temperatures in the Midwest/East this weekend will also shift back
toward the west with time. Rainfall will focus over the northern
Tier (Upper Midwest/Great Lakes) then into the Midwest and Mid-
Atlantic by midweek, across the Southeast, and over the Southwest
that may wane by the middle of next week.


...Guidance/Predictability Assessment...

Through the 12Z/18Z guidance, a consensus blend approach worked
well for a starting point to the fronts/pressures and sensible
weather (via the 01Z NBM). One difference to note was between the
ECMWF EPS and AIFS ENS mean with the 500mb pattern -- the latter
being stronger with the upper low west of British Columbia but then
less amplified downstream with both the ridging and troughing into
the Northeast and Atlantic Canada. This may insinuate that
embedded shortwaves may act to put some wrinkles in the flow (and
predictability) east of the Rockies.

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...

Over the weekend there are three regions where there may be
excessive rainfall and isolated areas of flash flooding -- the
Upper Midwest, Southeast/northern Florida, and the Southwest. Over
the northern region, a wavy frontal boundary will act as a focus
for showers and thunderstorms with locally heavy rainfall. Some of
the models show multi-inch amounts, but vary quite a bit in
placement. Future upgrades to a Slight Risk are likely should the
guidance remains consistent or increase amounts, but would like to
see a little more convergence in location. Persistently high
moisture levels over the Southeast, 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. The
last area (Southwest) will see a continued surge in moisture
Sat/Sun, but with a slight shift eastward next week. Some storms
will be capable of producing heavier rainfall that may fall over
more sensitive areas (steep terrain, in/around burn scars, etc.).
For the rest of the period, rainfall may ease a bit in the
Southwest but remain widespread across the Upper Midwest/Great
Lakes/Midwest as the frontal boundary wavers across the region then
slowly moves southward midweek next week.

Very warm temperatures will persist over much of the central and
eastern U.S. this weekend, 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 and humidity will combine to make for very
uncomfortable conditions as well over the Lower MS Valley/Florida
this weekend into next week. With the cold front approaching from
the north, cooler air filtering in will provide some degree of
relief from the Great Lakes to the Northeast next Tues/Wed. For the
West Coast, the weekend will be much cooler than mid-August
values; however, temperatures are expected to slowly rebound next
week 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.


Fracasso


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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