ACUS02 KWNS 120602
SWODY2
SPC AC 120600

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
0100 AM CDT Fri Jul 12 2024

Valid 131200Z - 141200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE NORTHERN
PLAINS INTO THE UPPER MIDWEST...

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

...Synopsis...
Upper ridging is forecast to be centered over the Four Corners early
Saturday morning, remaining largely in place for the remainder of
the period. An upper trough is expected to progress through
north-central Canada, contributing to moderate westerly mid-level
flow between this trough and the Four Corners ridging. A shortwave
trough will likely move through this westerly flow, progressing
across the northern Plains/southern Canadian Prairie Provinces into
the Upper Midwest. Primary surface low associated with this wave
will likely move just ahead of it from central Manitoba into far
northwestern Ontario. A secondary surface low may develop at the
triple point, with this low likely moving from central ND eastward
across northern MN.

Farther east, a shortwave trough is forecast to progress eastward
from southern Quebec/western NY across the Northeast while
subtropical ridging persists over the Southeast.

...Eastern Dakotas into the Upper Midwest...
A very moist airmass will likely be in place from the eastern
Dakotas into the Upper Midwest on Saturday morning, preceding the
shortwave trough and associated surface features mentioned in the
synopsis. Some isolated thunderstorms may be ongoing across MN early
Saturday morning, supported by warm-air advection throughout the
warm sector. Evolution of this early morning convection is
uncertain, but it will likely shift gradually southeastward
throughout the morning, potentially persisting long enough to become
surface-based in the northeast IA/southern WI/northern IL vicinity.
If this scenario is realized, the primary severe threat would be
damaging gusts.

Afternoon thunderstorm development also appears probable across
western MN as the surface low interacts with the warm and moist
airmass expected to be in place. Surface temperatures in the mid to
upper 80s/low 90s amid upper 60s/low 70 dewpoints will support
strong to very strong buoyancy, with MLCAPE over 3000 J/kg probable.
Moderate vertical shear is anticipated across the region, but
precipitation-laden updrafts are still expected to promote a
predominantly outflow-dominant storm mode. Some outflow amalgamation
is possible, with the resulting convective line then progressing
southeastward into west-central WI. Primary severe threat is
damaging gusts, but isolated large hail is possible with early
cellular development. Outflow-dominant storm mode should keep the
tornado threat low, but more southerly flow is possible near the
surface low, with surface vorticity greater in this region as well.
This could result in some low-probability tornado potential.

...Northeast MT into northern ND...
Combination of low-level convergence along the lee trough and
moderate low-level moisture (likely via post-frontal upslope flow)
may result in convective initiation over northeast MT. Easterly
low-level flow veering to westerly aloft will support strong
vertical shear capable of maintaining a supercellular storm mode.
Large hail and/or damaging gusts are the primary risks with these
storms as the move eastward into northwest/northern ND.

...Western/Central SD and the NE Panhandle...
Isolated thunderstorm development is possible Saturday afternoon
amid the low-level convergence across western SD and the NE
Panhandle. High cloud bases and moderate northwesterly flow aloft
could support a few strong downbursts with any more robust
convection.

...Lower MO Valley/Ozark Plateau into the Lower OH Valley...
Thunderstorms may be ongoing over the Lower MO Valley/Ozark Plateau
early Saturday morning, supported by warm-air advection associated
with the low-level jet. These storms will likely be sub-severe, but
an associated convectively induced vorticity maximum may drift
eastward throughout the day, leading to additional storm development
during the afternoon across the Lower OH Valley. Current expectation
is that modest vertical shear should limit the severe potential
within these storms.

..Mosier.. 07/12/2024

$$
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