957
FXUS02 KWBC 251854
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
254 PM EDT Wed Jun 25 2025

Valid 12Z Sat Jun 28 2025 - 12Z Wed Jul 02 2025

...Overview...

A broad dome of high pressure with above average 500mb heights over
the South/Southeast will shunt troughs and associated fronts
across the northern tier states. These northern shortwaves will
support fronts and rounds of possibly heavy rain across the
Northeast Saturday and in the north- central U.S. Saturday-Sunday.
Above average temperatures may linger in the Midwest to Carolinas
and possibly compound heat stress for areas that have been seeing
extreme heat. Upper troughing may deepen some as it digs into the
Great Lakes/Ohio Valley/Northeast, pushing a cold front gradually
southeast. Hot temperatures and scattered to widespread showers and
thunderstorms are likely ahead of the front across the central
U.S. to Eastern Seaboard.

Further west, monsoonal moisture is expected to increase for the
Southern/Central Rockies and adjacent High Plains, while the West
should see increasing heat underneath an upper ridge.


...Guidance/Predictability Assessment...

The latest suite of guidance continues to have a decent handle on
the synoptic pattern with the southern tier ridging and an active
northern stream. All indicate the trough tracking from the Northern
High Plains Sunday through to the Great Lakes/Northwest Tuesday
and Wednesday will deepen somewhat and usher in rounds of heavy
rainfall with the potential for local flash flooding concerns,
particularly for the north-central states. Subtleties in the
details persist which will affect the exact location and timing of
frontal features, sensible weather and precipitation amounts. Once
the trough reaches the East and ridging expands into the Four
Corners region. A southern stream trough gradually approaches
California while a northeastern Pacific upper low may send
(uncertain) shortwaves toward the Northwest next week.

As previously noted, the CMC pushed the northeastern Pacific low
progressively into Canada while the rest of the solutions held
back. Towards middle/latter periods the CMC was out of phase with
the broader model consensus. The WPC preferred blend started with a
multi-model compromise that trended toward an EC/GFS and ensemble
means solution.


...Weather/Hazards Highlights...

An initial shortwave and weak low pressure system along a frontal
boundary could bring locally heavy rain in the Northeast lingering
into Saturday. Ample moisture (PWs likely over the 90th percentile)
and some instability could allow for heavy rain rates and possible
flash flood concerns. WPC held onto the Marginal Risk in the Day
4/Saturday ERO for this activity with minor expansions made for
this issuance. Farther west, thunderstorms are likely to form
ahead of the broader upper trough and the surface frontal boundary
in the northern Plains to Upper Midwest Saturday. Global models
have already been showing high instability with MUCAPE 4000-6000
J/kg for this region, so severe storms are likely, and this will
also support heavy rain rates that could cause flash flooding. A
similar setup is likely on Sunday, just with the cold front a bit
more progressive southeastward. This allows for a broad Marginal
Risk in the Upper/Middle Mississippi Valley back into the central
Plains for the Day 5/Sunday ERO. The latest guidance and WPC QPF
supported the expansion of the Marginal Risk across Wisconsin and
Michigan. Further refinements may be needed in future cycles since
there is uncertainty in the placement of heaviest rain.

Over the weekend into early next week, scattered thunderstorms are
likely farther south in the broad warm sector as well. There will
be less forcing for organization and sustaining of storms across
the central and southern tier away from the upper jet, but
instability could allow for heavy rain rates that may cause nonzero
chances of localized flash flooding, but that are likely dependent
on smaller scale boundaries and are less predictable at this
point. One area of focus that the models show for some heavier rain
is across the central to eastern Gulf Coast region. Will monitor
if there will be flash flooding concerns there but it would have to
battle with very high flash flood guidance. Into the workweek as
the main cold front continues to press south and east, heavier rain
and thunderstorms could stretch across the south-central Plains
into the Ohio/Tennessee Valleys and into the East.

Monsoonal type moisture is likely to increase over the
Southern/Central Rockies and Plains where there could be a
weakness in the upper ridge. On Saturday main flash flooding
concerns will be across the Sacramento Mountains, where the steep
terrain and burn scars cause the area to be particularly sensitive
to rain, so WPC is covering this with a small Marginal Risk in the
Day 4 ERO. But moisture levels and thus coverage and rain amounts
of storms should increase into early next week. A Marginal Risk is
in place across eastern New Mexico and far West Texas in the Day
5/Sunday ERO with this activity. These areas are seeing heavy rain
in the near term, and the wetter antecedent conditions enhance
flash flooding concerns.

By the weekend, heat will be much less extreme than currently, but
above average temperatures by 5-12 degrees are likely across the
north-central U.S., Mississippi Valley, and into southern parts of
the Mid-Atlantic. HeatRisk shows some Major (level 3 of 4) areas in
these regions, indicating heat levels that affect anyone without
effective cooling and/or adequate hydration. Meanwhile the
Northeast will be much cooler behind a backdoor cold front. Into
next week, slightly above average temperatures will shift east
ahead of a cold front and moderate. Farther west, building heat is
expected next week as an upper ridge takes hold. Temperatures in
the Northwest are likely to be 10-15 (locally 20) degrees above
normal, for highs nearing 100F. In the Desert Southwest,
temperatures a few degrees above already high averages will equate
to 100s and 110s. Moderate to Major HeatRisk is shown for much of
the Interior West.


Campbell/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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