882
ACUS01 KWNS 150554
SWODY1
SPC AC 150552

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1252 AM CDT Tue Jul 15 2025

Valid 151200Z - 161200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS IN PARTS OF
NE...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SEPARATELY IN
WY...

...SUMMARY...
Scattered severe gusts, some significant, and large hail are
probable across parts of Nebraska this evening. A mix of scattered
damaging winds and severe hail are possible from the Upper Great
Lakes into Wyoming this afternoon to mid-evening.

...Synopsis...
A positive-tilt shortwave trough over the northern Rockies will
pivot eastward into the northern Great Plains by early Wednesday.
Low-amplitude shortwave impulses will persist downstream across the
southern Canadian Prairies and northern ON. Multiple MCVs will drift
east from the central Rockies to Upper Midwest.

As surface ridging builds down the High Plains today, a lee cyclone
should be centered over the central High Plains this afternoon. The
slower-moving portion of the cold front will extend northeast
towards Lake Superior. This boundary should become more wavy as
extensive convective outflows occur by evening.

...NE/SD...
A rather favorable thermodynamic environment will exist ahead of the
aforementioned surface low and front by peak heating. Hot and
deep-mixed thermodynamic profiles will overlap the western periphery
of rich low-level moisture over the eastern plains. Amid very steep
mid-level lapse rates, a corridor of large buoyancy with MLCAPE of
2500-3500 J/kg should develop from central NE into southern SD.
While mid-level westerlies should be weak, increasing speed shear
will exist into the upper levels, fostering large hail growth in
initial cells.

Scattered thunderstorms are expected along the nose of the low-level
thermal ridge as a minor mid-level impulse near the MT/WY border
shifts east into central SD during the late afternoon to early
evening. Progressively higher-based storms should flank to the
southwest towards the lee cyclone. Pronounced low-level convergence
along the front is expected through the evening. This setup should
favor the large hail threat transitioning to upscale growth and a
potential severe MCS. ARW-NSSL forecast soundings indicate potential
for a 75-kt rear-inflow jet, which would be conducive to significant
severe surface gusts. The most likely corridor for these to occur is
centered on the central NE vicinity. This MCS may persist overnight
but should wane owing to lessening instability/increasing MLCIN.

...Upper Great Lakes/Midwest...
Remnants of ongoing convection are expected to be ongoing at 12Z
across the northeast MN/far northwest WI/western Lake Superior
vicinity. This activity may persist into late morning but should
diminish/shift east of the international border. The trailing
outflow-reinforced front will be the focus for renewed storm
development during the afternoon. The most likely corridor is from
central MN into western Upper MI, as an MCV approaches from central
SD. Guidance varies on the degree of timing, but early afternoon
initiation appears plausible. In west-central MN to eastern SD,
guidance has more spread in the degree of convective coverage along
this portion of the front, likely related to MCV timing. Ample
buoyancy south of the boundary in MN to northwest WI will foster
potential for an initial hail threat before multicell clusters yield
sporadic damaging winds.

...WY to eastern Great Basin...
Mid-level height falls attendant to the aforementioned northern
Rockies shortwave trough will favor scattered to widespread
thunderstorms, peaking in the late afternoon to early evening. The
highest probability of organized storms will be across WY, as a
compact 40-50 kt jetlet becomes centered near the Yellowstone
vicinity. Downstream surface ridging will modulate the northeast
extent of severe potential. But a confined corridor centered along
the surface front should be favored for an organized cluster. With
inverted-v thermodynamic profiles south of the front, a swath of
severe gusts and isolated severe hail are possible from 22-03Z.

Very deeply mixed thermodynamic profiles will be prevalent into
parts of UT to northeast NV. Weak deep-layer shear will yield
disorganized cells, but any of this activity will be capable of
erratic severe gusts.

...Southeast AZ...
Weak mid-level east-northeasterlies and a hot boundary layer could
support localized severe gusts from late afternoon through dusk.

..Grams/Thornton.. 07/15/2025

$$