202
ACUS01 KWNS 151236
SWODY1
SPC AC 151234

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0734 AM CDT Tue Jul 15 2025

Valid 151300Z - 161200Z

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

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
WYOMING...

...SUMMARY...
Scattered severe gusts (some 75+ mph) and large hail are probable
across parts of Nebraska late this afternoon and evening. A mix of
scattered severe/damaging winds and large hail should also occur
from the Upper Great Lakes to Wyoming this afternoon to mid-evening.

...Northern/Central Plains to the Upper Great Lakes...
A belt of stronger mid-level westerly flow will remain confined
generally along/north of the international border today. Even so,
multiple weak mid-level perturbations, some of which are related to
prior/ongoing convection, will aid in additional thunderstorm
development later this afternoon and evening across portions of the
northern/central Plains to upper Great Lakes. This convection will
also be aided by a slowly southward sagging cold front across SD
into NE, as a weak low develops northeastward across the Upper
Midwest into Canada along this boundary. As diurnal heating occurs
today, a moist and moderately to strongly unstable airmass will
exist by this afternoon along/south of the front from NE into parts
of SD, MN, and the U.P. of MI. While stronger flow aloft will tend
to remain to the north of the front, there should still be
sufficient deep-layer shear across the warm sector for some updraft
organization.

Current expectations are for robust thunderstorms to develop along
the front in MN by early afternoon, and quickly spread eastward
across northern WI, the U.P. of MI, and Lake Superior through the
rest of the afternoon into the evening. 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 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 and ample instability. 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 upper trough digging southeastward over the northern Rockies
today will influence convective development this afternoon across
parts of the northern Great Basin and WY vicinity. High-based
convection that occurs across parts of eastern NV into UT will occur
in a relatively dry profile, with limited total precipitable water.
Still, a deeply mixed boundary layer coupled with weak instability
should support some risk for severe gusts with this activity as it
moves generally east-northeastward this afternoon/evening across the
northern Great Basin vicinity.

Greater low-level moisture, with surface dewpoints generally in the
low to mid 50s, is already present this morning over parts northern
WY. Convection that initially develops near Yellowstone in northwest
WY may grow upscale fairly quickly into an organized cluster 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. The Slight Risk
across WY has been expanded northward/eastward some based on latest
guidance trends. This cluster should eventually weaken late this
evening/tonight as it approaches the WY/NE/SD border vicinity.

...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.

..Gleason/Bentley.. 07/15/2025

$$