382
FXUS02 KWNH 310718
PREEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
318 AM EDT Thu Jul 31 2025

Valid 12Z Sun Aug 03 2025 - 12Z Thu Aug 07 2025


...Overview...

Early next week, broad upper troughing will be present over the
east-central to eastern U.S. while an upper ridge over the
Rockies/High Plains is anchored by a Southwest upper high.
Disturbances moving through the general northwest flow on the
eastern side of the ridge should trigger rounds of thunderstorms
and possibly heavy rain across portions of the Plains into Sunday.
Meanwhile a stalling front across the Southeast should promote
additional rounds of heavy rain in its vicinity. Combining energies
will allow for increased rain chances for much of the east-central
and eastern U.S. as the week progresses. Troughing over the
Northwest early next week should send shortwaves across the
northern tier, but in general the trough looks to become more
shallow as the Southwest upper high grows and causes average to
above average August heat for the Southwest into the Plains.


...Guidance/Predictability Assessment...

Model guidance shows typical levels of agreement during the medium
range period, with the larger scale features generally agreeable
but with differences in the details. The Southwest upper high of
594+ dm has the best agreement of expanding in size across the Four
Corners and southern Plains as next week progresses, in a classic
early August pattern. Shortwave and longwave troughs rotating
around the ridge show less consensus though. On the broad scale,
models show troughing deepening in the eastern U.S. by Monday-
Tuesday, and recent 00Z model runs maintain its depth longer than
the 12/18Z model cycles. There are typical detail differences in
the exact axis of this trough especially across the northern tier
by around Tuesday. 12/18Z GFS runs were slower than the EC/CMC, but
the newer 00Z models seem more agreeable. These discrepancies
affect the possibility of a weak surface low in the east-central
U.S. and the QPF pattern and amounts. In the Northwest, initial
troughing is forecast to lift as the week progresses, with
differences in a possible shortwave moving eastward across the
northern tier.

With the okay agreement overall but the detail differences, the
WPC forecast favored a blend of the 12Z ECMWF, 18Z GFS, and 12Z
CMC early in the forecast period, and used the ensemble means
increasingly going forward, with the means reaching half the blend
by Day 7 to temper the solutions of any individual model.


...Weather/Hazards Highlights...

A cold front will make its way farther south than is common for
early August, located around northern Florida and across the
central Gulf Coast by Sunday at the leading edge of the upper
trough. High moisture content and instability near the front will
allow for some localized heavy rain, which could cause a flash
flooding risk especially after rain from the previous day or two
could make antecedent conditions wetter. A Marginal Risk is in
place across northern Florida into southeastern Alabama and
southern Georgia and South Carolina on Day 4/Sunday, and will
continue into Day 5/Monday as the front stalls into the workweek.

Farther west, shortwaves rounding the eastern edge of the upper
ridge in the Rockies/High Plains are forecast to interact with the
same front that bends back across the Great Plains. Rounds of rain
and thunderstorms are likely to continue into Sunday with possibly
multiple MCSs. Above normal moisture and instability should support
high rain rates at times. A broad Marginal Risk on Day 4/Sunday
covers much of the Plains from the TX/OK Red River north into the
Dakotas, with just a bit of the Mississippi Valley covered due to
isolated flash flooding concerns. No Slight Risk areas are noted at
this time due to uncertainties in rainfall placement and the
localized/isolated nature of the thunderstorm complexes. Then by
Monday, there is a general trend for the Ohio/Tennessee Valleys to
see increasing rain and thunderstorms as the front moves east. The
upper trough will also deepen and provide a supportive dynamical
environment for thunderstorms, while a tongue of instability
reaches northward. So as a first take at the Day 5/Monday ERO, will
show the Marginal Risk from the Southeast drawn north across the
Tennessee Valley and Lower Ohio Valley. There remains uncertainty
with the details of QPF due to subtle differences in the shortwaves
and surface boundaries involved, so stay tuned for possible future
changes. Rain and storms are generally forecast to overspread the
east-central U.S. Tuesday and toward the Eastern Seaboard
Wednesday, with changes to the details likely.

Elsewhere, some rain and convection is possible across the
Interior Northwest coincident with the upper trough. By Monday
moisture and instability will be above normal for the northern
Rockies into the northern High Plains. A Marginal Risk is
delineated in the Day 5/Monday ERO for northwestern Montana as the
shortwave moves through and provides lift. Rain and thunderstorms
are expected to continue across the northern Plains and Midwest
Tuesday-Wednesday. Meanwhile, the Four Corners states could see
some increasing monsoon showers underneath the broad ridge, amid
the relatively dry monsoon season especially across Utah/Arizona.

Cooler than average temperatures are likely on the cool side of
the main frontal system early next week. The Southeast and much of
the central U.S. can expect highs of 5-10 degrees below average,
with locally greater anomalies, as highs only reach the 70s and low
80s for parts of the Southeast. These temperatures should
gradually warm closer to normal as the week progresses. The
Northwest will also generally be cooler than average under rounds
of troughing. The main hotspot for temperatures will be across the
Southwest, where lower desert areas can expect highs 105-115F, and
temperatures will be warming above normal into the southern and
central High Plains as the upper ridge expands. HeatRisk from the
Southwest into Texas shows some Major (level 3/4) areas. Florida is
forecast to see seasonable temperatures in the 90s, but with ample
humidity allowing for some areas of Major HeatRisk there as well.


Tate


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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