Subj : DAY1SVR: Day 1 Convective
To   : All
From : Mike Powell
Date : Tue Aug 20 2024 07:37:00

ACUS01 KWNS 200544
SWODY1
SPC AC 200542

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1242 AM CDT Tue Aug 20 2024

Valid 201200Z - 211200Z

....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
MONTANA...

....SUMMARY...
Widely scattered to scattered storms are possible in parts of
central/eastern Montana with more isolated coverage into parts of
the central High Plains. Severe winds and large hail are the primary
threats.

....MT into the Central High Plains...

Upper ridge is forecast to hold across the High Plains through the
day1 period, though some weak mid-level height falls are expected
across the northern Rockies in response to a very weak disturbance.
With broad southwesterly flow entrenched across the northern
intermountain region into central MT, a surface lee trough will arc
from central MT-western Black Hills-eastern CO. This will ensure
southeasterly boundary-layer winds are maintained across the
northern High Plains into central MT. Strong surface heating will
allow temperatures to warm into the 90s across eastern MT and
convective temperatures should be breached at lower elevations by
20z. Latest thinking is scattered convection will develop over the
higher terrain of southern MT then spread northeast toward the High
Plains. NAM forecast sounding for LWT at 20z exhibits 2300 J/kg
MLCAPE with 0-6km bulk shear around 50kt. This profile suggests
supercells are likely, especially early in the convective cycle.
Relatively high cloud bases favor strong gusts and this should be
the primary risk, though large hail is certainly possible with
supercells. Scattered convection should spread toward eastern MT
where gradual weakening is expected during the late evening.

Farther south, a very weak disturbance will rotate around the
southern Rockies anticyclone into eastern CO by late afternoon.
Scattered convection should easily develop over the higher terrain
of southern CO then spread east along/north of a front that will be
draped from northwest OK into southeast CO. Favorable veering wind
profiles with height, along with 0-6km shear on the order of 30kt,
suggests slow-moving supercells could spread east-southeast during
the late afternoon/evening. Isolated hail/wind are the primary
threats.

...Darrow/Halbert.. 08/20/2024

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