ACUS02 KWNS 180541
SWODY2
SPC AC 180539

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1239 AM CDT Fri Jul 18 2025

Valid 191200Z - 201200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SATURDAY INTO
SATURDAY NIGHT ACROSS PARTS OF EASTERN IOWA...SOUTHERN
WISCONSIN...NORTHERN AND CENTRAL ILLINOIS AND INDIANA...CENTRAL AND
SOUTHERN LOWER MICHIGAN...NORTHERN AND WESTERN OHIO...PARTS OF
NORTHWESTERN PENNSYLVANIA AND WESTERN NEW YORK STATE...

...SUMMARY...
Strong thunderstorms, including one or two organizing clusters, are
possible across southern portions of the Great Lakes region and
adjacent portions of the Ohio Valley Saturday into Saturday night,
with more widely scattered strong thunderstorm development across
the northern Rockies into adjacent high plains.

...Discussion...
Models indicate that at least some amplification to the mid/upper
flow across the northern tier of the U.S. is probable during this
period. It appears that this will include digging troughing across
the Pacific Northwest through northern Rockies, downstream of
increasingly prominent ridging building across the northeastern
Pacific. Farther east, troughing is forecast to dig across and to
the east of the Great Lakes, in advance of significant troughing
within a separate branch of westerlies, pivoting southeast of Hudson Bay.

In lower levels, the better defined remnants of an ongoing cold
frontal intrusion to the lee of the Rockies, perhaps aided by
stronger differential surface heating during the day Saturday, may
shift east of the middle Mississippi through the lower Ohio Valley.
At the same time, a reinforcing intrusion of cooler and drier air is
forecast to advance across and south of the Upper Midwest and Great
Lakes, probably in the wake of a weak eastward migrating surface low.

...Midwest through Great Lakes/Ohio Valley...
Model depictions concerning synoptic and sub-synoptic features,
including potential convective evolution remain rather varied. In
general, it appears that low-level moistening ahead of the
reinforcing cold front will contribute to moderate destabilization
as far north as the southern Great Lakes during the day Saturday.
On the southern fringe of the stronger westerlies, 30-50 kt flow in
the 850-500 mb layer across southern Wisconsin and Lower Michigan
into the lower Great Lakes will contribute to potential for
organized convective development. This may include a couple of
supercells and perhaps an upscale growing cluster. Although
mid-level lapse rates may be modest, this may be accompanied by some
risk for hail, in addition to strong to severe surface gusts and
perhaps a tornado or two.

Southwestward toward the middle Mississippi into Ohio Valleys,
deep-layer mean wind fields are likely to be weaker, but shear
beneath west-northwesterly mid-level flow may still support
potential for organized thunderstorm development, in the presence of
a seasonably moist boundary-layer becoming characterized by sizable
CAPE with daytime heating. Forcing for this activity remains
unclear, and probably will hinge on convectively generated or
augmented perturbations migrating around the northern periphery of
mid/upper ridging encompassing much of the central and southern tier
of the U.S. to the east of the Rockies.

...Lee of the northern Rockies...
Downstream of the digging mid/upper troughing across the Northwest,
moisture return to deepening lee surface troughing is forecast to
contribute to at least a narrow corridor of moderate to large
mixed-layer CAPE, in the presence of steep lower/mid-tropospheric
lapse rates. Veering of winds with height probably will contribute
to sufficient shear for organized thunderstorm development,
including supercells, as widely scattered to scattered thunderstorms
develop off the higher terrain into the high plains late Saturday
afternoon and evening. It is possible that severe weather
probabilities could still be increased in later outlooks for this
period.

..Kerr.. 07/18/2025

$$
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ACUS02 KWNS 060532
SWODY2
SPC AC 060530

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1230 AM CDT Sat Jun 06 2026

Valid 071200Z - 081200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ...

...SUMMARY...
Scattered severe storms capable of large to very large hail, severe
wind gusts, and perhaps a tornado or two are possible across the
northern Plains. More isolated severe storms capable locally
damaging wind gusts may occur across portions of the Mid-Atlantic. A
brief tornado or two appears possible in eastern Oklahoma and
western Arkansas.

...Synopsis...

A vorticity maximum and associated mid/upper-level jet streaks
within the base of broader-scale troughing from the lee of the
Canadian Rockies into northern Intermountain Region Sunday morning
are forecast to accelerate northeast through the northern High
Plains, ahead of an upstream jet segment moving onto the Pacific
Northwest coast. Elsewhere, an amplified short-wave trough will
progress through the Northeast, while a more loosely organized
trough progresses through the central and southern Plains through
the Ozarks and mid MS Valley.

At the surface, an area of low pressure and associated pre-frontal
trough over the western Dakotas will be overtaken by a cold front
moving out of the northern Rockies. That frontal system will
continue east into the ND-MN Red River Valley, and southeast into
the central High Plains by Monday morning. Elsewhere, more of a
backdoor cold front will progress south/southwest through the
Northeast into Mid-Atlantic.

...Montana and Wyoming into the Dakotas...

A hot, deeply mixed boundary layer is expected to develop ahead of
the pre-frontal trough over the western Dakotas Sunday afternoon,
with the presence of steep low/mid-level lapse rates contributing to
an axis of moderate to strong instability. Moderate instability is
expected to extend into eastern MT and northeast WY, owing to
low-level moisture wrapping around the surface trough. Initial storm development is expected by mid afternoon along the western fringe of
the instability axis across southeast MT into north-central and
northeast WY as lift is enhanced by terrain, the cold front, and
forcing tied to the vorticity maximum and attending jet streaks. A
separate thunderstorm regime is expected to evolve by late afternoon
into evening over the western Dakotas as the cold front merges with
the pre-frontal trough.

The MT/WY storms are expected to mature in a strongly sheared
environment, which will favor supercells capable of large hail.
Initially marginal vertical shear with the western Dakotas storm
regime is expected strengthen through the evening, supporting the
potential for supercells capable of large to very large hail and
severe wind gusts as the primary hazards. Some tornado threat may
materialize by mid/late evening across portions of north-central ND
where strengthening low-level shear will coincide with a more moist,
lower-LCL boundary layer. The magnitude of the threat will be
contingent on storm mode at that time, given the tendency for more
linear forcing along the cold front.

... Central Virginia into the Chesapeake Bay Area...

Daytime heating coupled with dewpoints in the 60s will contribute to
a moderately unstable air mass by afternoon, ahead of a pre-frontal
wind shift moving into the area from the north. Convergence along
that boundary along with the glancing influence of the mid-level
trough passing to the immediate north are expected to support
isolated to widely scattered thunderstorms during the afternoon
across the discussion area. Relatively warm mid-level temperatures
are expected to limit the potential for large hail; however, the
presence of steep, low-level lapse rates and 30-35 kt of
northwesterly deep-layer shear appear supportive of locally damaging
wind gusts through the afternoon into early evening.

...Eastern Oklahoma and Western Arkansas...

Forcing for ascent attendant to a vorticity maximum moving through
the base of broader-scale troughing is expected to contribute to an
increase in thunderstorm coverage early in the day. That scenario
would tend to limit air mass destabilization through the afternoon,
leaving severe-storm potential in question. However, there is a
signal in some guidance that a low-level jet will strengthen during
the afternoon into evening, leading to an increase in low-level
shear. A concurrent risk for a brief tornado or two may materialize,
especially with any storms on the southern or western fringe of the
larger convective footprint. That notion is generally supported by
the 00z HREF mean 0-1 km SRH, which shows values increasing to
100-150 m2/s2 by Sunday evening.

..Mead.. 06/06/2026

$$
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