835
FXUS02 KWNH 300719
PREEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
318 AM EDT Wed Jul 30 2025

Valid 12Z Sat Aug 02 2025 - 12Z Wed Aug 06 2025

...Heavy rain and flash flooding potential for the Southeast into
the weekend...

...Overview...

A reasonably strong cold front for early August is forecast to
push into the Southeast at the leading edge of an upper trough into
the weekend. Moisture and instability along and ahead of the front
will promote heavy to excessive rainfall in thunderstorms that
could cause localized flash flooding. The front and upper trough
should also displace the upper ridging which is responsible for the
heat wave in the short term, limiting the heat to Florida Saturday
Friday and lessening in scope and magnitude early next week. The
front will stretch westward into the south-central U.S. and bend
northward across much of the Plains. Complexes of showers and
storms are likely in the central U.S. for multiple days due to the
front as well as shortwaves moving through the flattening upper
flow. Rain and thunderstorms chances are likely to increase across
the east-central and eastern U.S. into next week.


...Guidance/Predictability Assessment...

Model guidance starts the medium range period in reasonably good
agreement on the larger scale. A general southern U.S. upper ridge
will become more limited to the Southwest by early next week as
models show lowering mid-upper heights in the Southeast, though
with some model spread in exactly how much the trough in the
Southeast deepens. Meanwhile ridging in the north-central U.S. is
likely to get suppressed by shortwaves over the weekend, but with
ample uncertainty in the details. Recent models generally show some
troughing forming from shortwaves over the Midwest early next week
with a gradual trek east, possibly helping create a weak surface
low pressure system. Meanwhile farther west, there has been some
model spread about upper troughing in the Northwest for the past
several days. Recent 00Z model guidance shows fairly good consensus
through early next week, but with some spread after that with how
much energy lingers near the West Coast and how much tracks
eastward across the northern High Plains -- CMC runs in particular
favor the eastern shortwave but the 00Z GFS/ECMWF have some
semblance of it as well. South of these features, the 594+ dm
subtropical ridge will start to expand over the Southwest to
southern Plains by midweek in a classic early August pattern.

Given the general model agreement early in the period, started the
WPC forecast with a multi-model blend of the individual models.
Used the ensemble means and increased their proportion to about
half Day 6 and more Day 7 to temper the solutions of any individual
model, with the increasing spread especially with the details
during the late period.


...Weather/Hazards Highlights...

The cold front pushing through the Southeast will provide a focus
for ample moisture and instability to pool while the right entrance
region of the upper jet should provide dynamical support. High
rain rates in widespread thunderstorms should lead to a flash
flooding risk -- a Slight Risk remains in place in the Day
4/Saturday ERO for Georgia into southern South Carolina. The front
stretching west across the Gulf Coast states in a moist and
unstable environment could promote scattered diurnal thunderstorms
into Saturday, and a Marginal Risk is in place in the Day 4 ERO due
to high rain rates that may overcome the high Flash Flood Guidance
and/or fall atop urban areas. By Sunday, the front will push south
a bit more and clear the central Gulf Coast from seeing much rain,
but thunderstorm chances linger from the Florida Panhandle
northward across parts of the Southeast. A Marginal Risk is
delineated for the Day 5/Sunday ERO for this activity. The front
stalling and meandering into early next week should maintain
scattered convection across the Southeast.

Farther west as the front bends back into the Plains, rounds of
rain and thunderstorms are likely with possibly multiple MCSs. Some
shortwave forcing and above normal moisture and instability should
lead to high rain rates, and some areas could see repeating rounds
of storms with the front stalling. Broad Marginal Risks cover much
of the Plains on Day 4/Saturday, as well as back into the northern
Rockies/High Plains near the back end of the front as much higher
than average instability (per the Extreme Forecast Index) lingers
before lessening early next week. No Slight Risk areas are noted at
this time due to uncertainties in rainfall placement and the
localized/isolated nature of the thunderstorm complexes. Also
looped the Marginal Risk around southeastern New Mexico where some
monsoonal moisture could linger Saturday and create isolated
flooding issues over sensitive burn scars. By Sunday the elongated
front is forecast to move a bit east, with the thunderstorm chances
moving with it. A Marginal Risk encompasses the Plains into parts
of the Mississippi Valley for the Day 5/Sunday ERO for likely
additional rounds of MCSs. The details are uncertain at this point,
but there is a general trend for the Ohio/Tennessee Valley into
the East to see increasing rain and thunderstorms by Monday-Tuesday
as the front continues moving east. Meanwhile the Southwest should
dry out around Sunday, but there may be a bit of a monsoonal
moisture return by Monday-Tuesday over Arizona/New Mexico amid the
relatively dry monsoon season especially across Utah/Arizona.

The cold front pushing through the Southeast will continue to
lessen the scope of dangerous heat into Saturday. Florida can
expect some heat to linger though, where HeatRisk remains in the
Major (level 3/4) and Extreme (level 4/4) categories, as
temperatures reach well into the 90s with higher heat indices
(nearing 110F), while morning lows well into the 70s and nearing 80
will not provide much relief. But thunderstorms are forecast to
increase in Florida early next week and limit extreme heat. Behind
the front, cooler than average temperatures (especially highs) are
likely. Into the weekend, highs of 5-10 degrees below normal are
forecast in the East, while much of the Plains can expect highs of
10-15 degrees below average, with highs in the 70s as far south as
parts of Kansas and Missouri. Temperatures should gradually warm
across those areas into early next week. Meanwhile the Northwest
can expect below normal temperatures as rounds of troughing move
through. But farther south, the Southwest can expect seasonable
heat (near to slightly above average), with the lower desert areas
seeing temperatures 105-110+ degrees.


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



$$