503
ACUS01 KWNS 151623
SWODY1
SPC AC 151621

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1121 AM CDT Tue Jul 15 2025

Valid 151630Z - 161200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FOR CENTRAL
NEBRASKA...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
SLIGHT RISK INTO THE UPPER MIDWEST...FOR NORTHERN AND EASTERN
WYOMING...AND NORTHERN UTAH AND SURROUNDING VICINITY...

...SUMMARY...
Scattered severe gusts (some 75+ mph) and large hail are probable
across parts of Nebraska late this afternoon and evening.  Scattered
severe gusts are also possible from the Upper Midwest to Utah and
Wyoming this afternoon to mid-evening.

...Northern/Central Plains to the Upper Midwest...
Primary focus for thunderstorms will be a slowly sagging,
southward-moving cold front across the Upper Midwest and a couple
mid-level perturbations moving east across the north-central states.
Radar imagery shows a convectively augment disturbance moving east
across northern SD and water-vapor imagery shows shortwave trough
moving east across southeast WY.  Both mid-level features will
likely prove instrumental in storm coverage and the risk for severe
activity later today.

Despite stronger mid-level westerly flow relegated north of the 48th
parallel, strong heating of a moist airmass will result in a very
unstable boundary layer by mid afternoon from the Upper Midwest
southwestward into the NE Sandhills.  Storms will probably develop
from eastern SD and into MN this afternoon near the front and ahead
of the SD mid-level feature.  Sufficient instability and
effective bulk shear should be present along/ahead of the front to
support organized convection, including some supercells. Large hail
will be possible with the initially semi-discrete thunderstorms,
before a rapid transition to a cluster/linear mode increases the
threat for severe/damaging winds. This activity should quickly
weaken by late evening as it encounters a less unstable airmass with
eastward extent across the upper Great Lakes.

A somewhat separate area of thunderstorms should initiate
along/south of the front across parts of southern SD into NE by late
afternoon/early evening. Greater instability will likely be present
across this region compared to locations farther north, but
deep-layer shear should be more modest (around 25-30 kt). Still,
some large hail may occur initially given the presence of steep
mid-level lapse rates. The threat for scattered to numerous
severe/damaging winds is expected to increase through the evening
across central NE as an intense bowing cluster develops and spreads
southeastward. Isolated significant gusts of 75+ mph appear possible
given the rather favorable thermodynamic environment.

...Great Basin into Wyoming...
The only change for this portion of the region is to increase
severe-wind probabilities across northern UT and surrounding states.
The southern fringe of stronger mid-level westerlies was sampled by
the 12 UTC Salt Lake City raob.  With the approach of the upstream
northern Rockies disturbance glancing the region later today,
short-term model guidance (e.g., HREF members, time-lagged HRRR) is
consistent in showing small clusters of storms moving east from
northeast NV/northwest UT eastward into northern UT/southeast ID/far
southwest WY.  Inverted-V profiles will strongly favor evaporative
cooling with the more rain-laden cores.  Scattered severe gusts are
possible with the more intense downbursts through early evening.

Farther east, the closer proximity to the upper trough digging
southeastward over the northern Rockies will promote scattered
storms across northern into eastern WY this afternoon and evening.
An organized cluster may evolve given 25-35 kt of deep-layer shear,
while posing a threat for mainly severe/damaging winds given the
presence of steepened low/mid-level lapse rates. Isolated large hail
may also occur.

...Arizona...
Modest mid-level east-northeasterlies will be present today across
parts of AZ on the southern periphery of a mid-level anticyclone
over the Southwest. Scattered thunderstorms should once again
develop this afternoon over the higher terrain of southeast AZ and
southwest NM. With very steep low/mid-level lapse rates expected
with ample daytime heating, this activity may pose an isolated
threat for severe winds as it spreads into the lower elevations of
southern AZ through the evening.

..Smith/Jirak.. 07/15/2025

$$