ACUS01 KWNS 131241
SWODY1
SPC AC 131240

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0740 AM CDT Fri Jun 13 2025

Valid 131300Z - 141200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
MONTANA...

...SUMMARY...
Scattered severe thunderstorms are expected this afternoon and
evening across parts of Montana, extending southward across portions
of the central/southern High Plains. The greatest concentration of
severe thunderstorms should occur across central/eastern Montana,
where large to very large hail, severe winds, and perhaps a few
tornadoes are anticipated.

...Northern Rockies/High Plains...
A closed upper low will remain centered off the coast of British
Columbia today, as multiple low-amplitude mid-level shortwave
troughs advance eastward across the Pacific Northwest to the
northern Rockies. A seasonably moist low-level airmass is already in
place this morning across much of MT, with surface dewpoints
generally in the 50s. Daytime heating and modestly steepened
mid-level lapse rates will aid in the development of moderate
instability by this afternoon, mainly from central MT eastward.
35-50 kt of west-southwesterly mid-level flow associated with the
shortwave troughs should support similar values of deep-layer shear,
with RAP forecast soundings showing long/straight hodographs at
mid/upper levels. Large-scale ascent attendant to the shortwave
troughs will likely encourage robust convective development by early
afternoon (18-20Z), initially over the higher terrain of the
northern Rockies.

This activity is forecast to quickly become supercellular given
moderate to strong effective bulk shear. The favorable lapse rates
and hodographs at mid/upper levels should support a threat for
scattered large to isolated very large (2+ inch diameter) hail with
this initially cellular activity. By mid to late afternoon into
early evening, some clustering/upscale growth is anticipated across
eastern MT and vicinity as low-level southeasterly flow gradually
strengthens. A greater threat for severe/damaging winds, with
isolated gusts of 75+ mph, remains apparent across this area. The
tornado threat is less clear, as the boundary layer is forecast to
become rather well mixed this afternoon. Still, modestly increasing
low-level shear this evening may support some threat for a few tornadoes.

...Central/Southern High Plains into Western Arkansas...
Elevated convection ongoing this morning across western OK in a
modest low-level warm advection regime may pose a limited severe
threat until it diminishes later this morning. Otherwise, at least
scattered thunderstorms should develop over the higher terrain of
the central Rockies and subsequently spread eastward into the
adjacent High Plains this afternoon and evening. Mid-level
west-southwesterly flow is generally expected to weaken with
southward extent across the central High Plains. But, sufficient
directional shear should still exist to support some updraft
organization, including the potential for a few supercells across
eastern WY/CO into western SD/NE/KS. Isolated large hail will be a
threat with any convection that can remain at least semi-discrete,
while severe winds may occur with one or more clusters that
eventually develop.

Convection is expected to become more isolated and less organized
with southward extent into the southern High Plains, but it may
still pose some hail/wind threat given sufficient instability and
steepened low/mid-level lapse rates. Somewhat stronger northwesterly
mid-level flow should also be in place across OK into western AR on
the back side of an upper trough over the lower/mid MS Valley. While
forcing will remain weak/nebulous across this region, a
conditionally favorable environment for severe thunderstorms will exist.

...Lower Mississippi Valley/Southeast into the Ohio Valley...
A weak mid-level trough will advance slowly eastward from the Ozarks
to the lower MS and OH Valleys through the period. Around 25-35 kt
of southwesterly mid-level flow will be present over these regions
as filtered daytime heating of a rather moist low-level airmass
occurs today. Even though lapse rates aloft are forecast to remain
poor, sufficient instability and deep-layer shear should exist to
support an isolated threat for mainly damaging winds this afternoon
and early evening as low-level lapse rates steepen. A Marginal Risk
has been included with this update across parts of the lower MS
Valley/Southeast into the OH Valley, where confidence in loosely
organized clusters occurring is greatest.

..Gleason/Kerr.. 06/13/2025

$$
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