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FXUS02 KWBC 291841
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
241 PM EDT Fri Aug 29 2025

Valid 12Z Mon Sep 01 2025 - 12Z Fri Sep 05 2025


...Overview...

A longwave trough amplifying over The West this weekend persists
through at least the middle of next week while troughing shifts
from over the Northeast this weekend to over the Great Lakes by
midweek where it amplifies into a deep low. A southern frontal
boundary will maintain rain and thunderstorm chances over the
Southwest and the Gulf Coast states. Shortwave energy coming off
the western ridge will support locally heavy rainfall over portions
of the central U.S. and the Tennessee Valley Monday-Tuesday. The
strong reinforcing upper shortwave/closed low pushing over the
Great Lakes will push a cold front across the central and eastern U.S.,
resulting in well below average temperatures down the Plains,
across the Midwest through the Appalachians and rain for the
Eastern Seaboard ahead of it Thursday-Friday.


...Guidance/Predictability Assessment...

Good agreement remains for the amplified upper pattern with the
ridge in The West (with a retrograding upper low moving up the BC
Coast Sunday-Wednesday) and broad troughing in the East that
becomes much deeper/closing into a low around the Great Lakes
midweek. Early next week, there remains some spread with the
departure of an upper level low from Maine with the ECMWF an
outlier there due to a much slower departure. Out West, there is
some agreement with a weak shortwave along the NorCal coast
Tuesday.

The main uncertainty in the period is with the deep Great Lakes
centered low around midweek with the ECMWF farther west/less
progressive with the trough axis than other global guidance. The
ensemble means were in relatively good agreement through that time,
but the 06Z EC-AIFS was notably closer to the GFS/CMC solution, so
a general model blend of deterministic guidance changed to one
favoring the ECENS/GEFS and the GFS/CMC starting on Day 5 for both
frontal positions and QPF.


...Weather/Hazards Highlights...

A surface front draped from the southern High Plains across the
Gulf Coast and through Florida will create a focus for monsoonal
and Gulf moisture early next week. The upper jet reaching the Gulf
Coast states, rather south for early August, should provide lift
for some thunderstorms and isolated heavy rain. A broad Day
4/Monday Marginal Risk ERO stretches from New Mexico and southeast
Arizona across southern/central parts of Texas and the Gulf Coast
through the Florida Peninsula for this activity. By Day 5/Tuesday
the front should clear much of the Gulf Coast, but Florida could
still see locally heavy rain, so will continue to delineate a
Marginal Risk there. The heavy rain focus in Florida remains
uncertain with multiple frontal boundaries moving through, so
future refinement is still expected. Rain chances look to
linger/shift south down the the Florida Peninsula through much of
next week. Meanwhile lingering monsoonal moisture continues to
warrant a Marginal Risk for Arizona/New Mexico on Tuesday, with a
note that the greatest moisture anomaly is over southern California
up through the Sierra Nevada.

To the north, a frontal system and a shortwave or two aloft will
support storms with higher rain rates across the Mid-Mississippi
Valley and the Tennessee Valley to Southern Appalachians on
Monday where Marginal Risks remain. By Day 5/Tuesday convection is
likely to focus a bit farther west from the Tennessee Valley to the
Mid-South where the Marginal Risk was shifted to. Meanwhile
enhanced moisture pushing across the Upper Midwest on Tuesday
ahead of the strong cold front continues to warrant a somewhat
targeted Marginal Risk over Minnesota into Wisconsin. The southern
extent of this risk area remains to be clarified by higher
resolution models with a bit of a southern expansion to the Iowa
border for now. As the cold front pushes eastward Wednesday, rain
and storms are forecast to overspread the east- central U.S. and
perhaps enhance along the Eastern Seaboard from low pressure
shifting north on Thursday.

The large trough covering the central and eastern U.S. next week
will promote below average temperatures. Temperatures around 5-10
degrees below normal will be fairly common east of the Rockies
early next week, but the reinforcing energy coming into the trough
will push a strong cold front into the north-central U.S. Wednesday
and through much of the Plains into the Midwest Thursday. Lows are
forecast to be generally around 10-15 degrees below average (with
frost potential Thursday morning around Lake Superior), while highs
could be around 15-20 degrees below normal. These cool highs could
set daily records for low maximum temperatures as highs only reach
the 50s in some locations of the Upper Midwest and Great Lakes. On
the other hand, the West can expect continued hot conditions under
the upper ridge. Temperatures will be most anomalous in the
Northwest, with upper 90s and possibly reaching 100F east of the
Cascades. Record high minimum and maximum temperatures are
possible, and the HeatRisk rebounds to Major to locally Extreme in
the northern Great Basin next week.


Jackson


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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