399
ACUS01 KWNS 130543
SWODY1
SPC AC 130541

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1241 AM CDT Sat Jul 13 2024

Valid 131200Z - 141200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE UPPER
MISSISSIPPI VALLEY AND NORTHERN PLAINS...

...SUMMARY...
Multiple clusters of strong to severe thunderstorms are possible
across portions of the Northern Plains into the Upper Mississippi
Valley today.

...Discussion...

Large-scale pattern is not expected to change appreciably over the
next few days as a dominant upper anticyclone is forecast to remain
centered near the Four Corners region. As a result, seasonally
strong mid-level flow will continue near the international border,
and several short waves will crest the western US ridge before
turning southeast toward the upper Great Lakes.

Boundary-layer moisture has increased considerably across the warm
sector of the northern Plains, where surface dew points are
currently in the lower 70s across much of the Dakotas. This airmass
is contributing to strong buoyancy, but much of this potential
remains unrealized, with only scattered thunderstorms ongoing early
this morning from extreme northwest NE-central Dakotas-western ON.
This activity is partly supported by a short-wave trough that is
beginning to turn southeast across southeast SK/western ND. Latest
model guidance suggests convection will be ongoing at the start of
the period over the northern Red River Valley. Diurnal heating will
contribute to strong instability downstream of this early-morning
complex. Models strongly suggest, to varying degrees, renewed
development will take place by early afternoon. This seems
plausible, and an MCS may ultimately evolve over central MN before
tracking toward northern IL during the overnight hours. Given this
scenario, damaging winds and hail would be the primary severe risks,
as supercells do not appear to be the primary storm mode.

Upstream across the northern High Plains, a secondary short-wave
trough is forecast to flatten the ridge over MT with 40-50kt 500mb
flow forecast to extend across central MT into the western Dakotas
by late evening. Strong surface heating will negate CINH across
north-central MT ahead of this feature, and thunderstorms should
easily develop near the MT/SK border by 19-20z as convective
temperatures are breached. NAM forecast sounding for CYXH (southeast
AB) at 19z exhibits MLCAPE on the order of 3000 J/kg with roughly
40kt surface-6km shear. Scattered supercells should evolve within
this airmass then track southeast. Hail could exceed 2 inches with
this early activity. When the convection grows upscale into an MCS,
a propensity for severe winds will become more common. Winds could
gust in excess of 70mph with any organized bowing squall structures.
MCS should propagate into SD during the overnight hours.

..Darrow/Moore.. 07/13/2024

$$