475
FXUS02 KWNH 290659
PREEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
259 AM EDT Tue Jul 29 2025

Valid 12Z Fri Aug 01 2025 - 12Z Tue Aug 05 2025

...Heavy rain and flash flooding potential in the
Carolinas/Southeast late week...

...Overview...

A reasonably strong cold front for late July-early August is
forecast to push into the Southeast at the leading edge of an upper
trough late week 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 upper ridging causing a heat
wave in the short term, limiting the heat to Florida/southern
Georgia Friday and gradually lessening in scope and magnitude by
the weekend. 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. back into the
northern Rockies for multiple days due to the front as well as
shortwaves moving through the flattening upper flow. Monsoonal
moisture could continue to cause showers and storms in parts of the
Southwest through late week with lessening rain chances by the
weekend.


...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
may be split by lower heights in the south-central U.S. at times,
and into early next week the eastern side of the 594+ ridge over
Florida and the Gulf should ease and leave the ridge more limited
to the Southwest. There is some uncertainty with how much heights
will lower in the Southeast by early next week though, with GFS
runs deepening the trough more than other guidance. Meanwhile
ridging will pass across the north-central U.S. late week, with
mean troughing in the Northwest. There is a general signal for the
central U.S. ridge to become suppressed by shortwaves by early next
week, but ample uncertainty in the details. Additionally, there
remain model differences with timing and amplitude of troughing
reaching the western U.S., as an upper low moves from the northeast
Pacific eastward across Southeast Alaska and into western Canada
with varied model solutions. The bulk of 12/18Z individual models
generally showed a more negatively tilted trough through western
Canada into the northwestern U.S. with its southern end moving more
quickly east, compared to the ensemble means that were more
neutral to positive with the trough axis. The newer 00Z guidance
fortunately seems to be closer to the ensemble means. The WPC
forecast used a multi-model blend early in the period, but
decreased the proportion of individual models in favor of the
GEFS/EC ensemble means as the period progressed, with the means
comprising just over half the blend Day 6 and more Day 7 given the
increasing model spread.


...Weather/Hazards Highlights...

The cold front pushing through the Mid-Atlantic to Southeast will
provide a focus for ample moisture and instability to pool while
there should be increasing dynamical support in the form of the
right entrance region of the upper jet. High rain rates in
widespread thunderstorms should lead to a flash flooding risk -- a
Slight Risk remains in place in the Day 4/Friday ERO for the
Carolinas to southern Appalachians. By Friday the front is forecast
to push a bit south, with the best focus for heavy rain and flash
flooding generally in South Carolina and Georgia, where a Slight
Risk is delineated for Day 5/Saturday. The front stalling there
into early next week could lead to additional convection. The front
stretching west across the Gulf Coast states in a moist and
unstable environment could promote scattered diurnal thunderstorms
there through late week into the weekend, and Marginal Risks are in
place in the Day 4/5 EROs due to high rain rates that may overcome
the high Flash Flood Guidance and/or fall atop urban areas.

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 Days 4 and 5 and 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 Risks are planned at
this time due to uncertainties in rainfall placement and the
localized/isolated nature of the thunderstorm complexes. Meanwhile
some monsoonal moisture is forecast to linger especially in New
Mexico on Friday, prompting a continued Marginal Risk there and
stretching into Colorado as the moisture meets the frontal system.
Moisture looks to become more limited to eastern New Mexico
Saturday and lessen even more early next week, furthering 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 late week. On Friday, heat will
be located across southern Georgia into Florida, 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. Florida may see hot
conditions continuing into Saturday as the front stalls north of
the state, but thunderstorm chances increase in Florida over the
weekend and early next week, which should 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 Kansas and the Oklahoma Panhandle. 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


$$