115
FXUS02 KWNH 200638
PREEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
237 AM EDT Sun Jul 20 2025

Valid 12Z Wed Jul 23 2025 - 12Z Sun Jul 27 2025

...Major heat wave building from the Southeast into parts of the
Central U.S. next week and beyond...

...Overview...

A large upper ridge will be anchored in place across the middle
Mississippi River valley through the end of the week, and this will
be the main driver in the heat wave that will be ongoing across
much of the nation east of the Rockies. By next weekend, the upper
ridge then becomes re-established over the Central Plains with a
weak trough over the Great Lakes and the Northeast states. An
active flow pattern aloft will continue across the northern tier
states and southern Canada, with a couple of cold frontal passages
expected. Out West, an upper trough with potential closed low is
likely near northern California, and a surface low along a
stationary front is likely near the Gulf Coast.

...Guidance/Predictability Assessment...

The 00Z model guidance suite and AIFS model features very good
overall synoptic scale agreement for the middle of the week, with a
general deterministic model blend working well as a starting point
in the forecast process. All of the guidance remains weak with any
surface low development over the northern Gulf, but with enough
moisture convergence and lift for heavy rainfall. By the end of the
forecast period next Sunday, the greatest model differences reside
across southern Canada with the timing and position of a low
pressure system and trailing cold front that will affect portions
of Montana and North Dakota. The ensemble means were gradually
increased to about 40% by this time.

...Weather/Hazards Highlights...

A cold front is progged to slowly drop southward across the Dakotas
and the Upper Midwest for the middle of the week, with a weak wave
of low pressure developing along it. This boundary will be
intersecting a warm and very humid airmass, and this is expected to
fuel the development of multiple thunderstorm complexes from
Nebraska to near Lake Superior Wednesday into Thursday. A Marginal
Risk area is valid for both Day 4 and Day 5 across much of this
region since some of the storms may have convective training, and
thus increasing the risk of localized flooding where this happens.
Improving conditions return to this region by Friday into next
weekend as a drier airmass settles in.

Another area of unsettled weather is expected to reside across
northern Florida and extending westward to the central Gulf Coast
mid to late week. A surface low is likely to form along a lingering
stationary front, and this should gradually track west through the
end of the week. There has been a modest increase in QPF associated
with this compared to the previous forecast issuance, but still
within the Marginal Risk category for Wednesday and Thursday with
the heaviest rainfall staying offshore during this time. The
rainfall potential continues into Friday as well, and this will
continue to be closely monitored in the days ahead. The potential
exists for several inches of rainfall in localized cases from
southern Louisiana to the Florida Panhandle, and a Slight Risk may
eventually be needed as the forecast guidance comes into better
focus in future model runs.

Elsewhere across the nation, moisture associated with the Southwest
U.S. monsoon will likely be reduced compared to recent days, with
some lingering showers/storms across New Mexico and into southern
Colorado, and affecting less of Arizona. However, there may be a
few convective cells that are slow moving across burnscar and other
sensitive areas, and therefore Marginal Risks remain prudent in the
excessive rainfall outlooks. Across New England, there will likely
be an axis of showers and thunderstorms moving in on Thursday, but
it currently does not look to cause much in the way of flooding
concerns.

The other big story will be the building heat across a large
portion of the east-central U.S. for the second half of the week
and into next weekend, courtesy of a large upper high becoming
anchored over the Mid-South. Heat Risk in the major category will
be prevalent from the Deep South to the Midwest and extending
eastward to include Tennessee and Ohio River Valleys to close out
the work week. Some of this heat will likely reach the East Coast
by Friday and next weekend following the pleasant stretch of
cooler weather for the first half of the week. Highs well into the
90s and even some low 100s will be commonplace from the Central
Plains to the East Coast, with the hottest readings across
Oklahoma, Texas, and Arkansas. It will also be uncomfortably warm
and humid at night, providing only limited relief from the heat.

Hamrick


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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