ACUS02 KWNS 121720
SWODY2
SPC AC 121718

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1218 PM CDT Fri Sep 12 2025

Valid 131200Z - 141200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE
SOUTHERN/CENTRAL HIGH PLAINS...PORTIONS OF THE NORTHERN PLAINS...AND
PARTS OF THE WESTERN GREAT LAKES/MIDWEST...

...SUMMARY...
Strong to severe storms are possible over parts of the southern and
central High Plains, northern Plains, and Midwest/Great Lakes on Saturday.

...Synopsis...
Persistent lee troughing will continue across the central/northern
Plains on Saturday as southwesterly flow aloft continues across the
central Rockies.  A weak cold front will move out of the Rockies and
into the central/southern High Plains Saturday afternoon. Across the
northern Plains/Upper Midwest, a warm front extending east from the
surface low will strengthen.

...Southern/central High Plains...
Forecast soundings across the southern/central High Plains indicate
widespread mid to upper-level clouds across the region Saturday
morning as convective debris from Day 1 convection across the
Southwest drifts slowly east. This will likely persist for much of
the day and limit overall heating. Despite this cloud-cover, weak to
moderate instability is forecast as temperatures warm into the low
70s with dewpoints in the upper 50s to low 60s and 500mb
temperatures around -10 C. Mid-level flow will strengthen through
the morning with effective shear around 30 to 35 knots during the
afternoon across eastern New Mexico, eastern Colorado and the
western OK/TX Panhandles. Limited buoyancy should keep the severe
weather threat mostly isolated. However, any pockets of
clearing/greater instability could support a more organized severe
threat in localized areas.

...Northern Plains...
Several rounds of thunderstorms will be possible across the Dakotas
on Saturday. 12Z CAM guidance has a consistent signal for elevated
thunderstorms Saturday morning across northern South Dakota where
isentropic ascent is maximized in a region with moderate instability
and moderately steep mid-level lapse rates and 40 to 45 knots of
effective shear. Some large hail will be possible during this
morning round of storms.

In the wake of this activity, moderate to strong instability is
forecast to develop across central/western South Dakota with minimal
inhibition by mid-late afternoon. Overall forcing will be subtle,
but weak height falls and a nearly uncapped environment may be
sufficient for isolated strong to severe storms Saturday
afternoon/evening with a conditional threat for large hail and
severe wind gusts given around 30 to 35 knots of effective shear.

Regardless of afternoon activity, an additional round of storms is
likely Saturday night as the primary mid-level shortwave trough
ejects from the Southwest into the central Plains. Strong height
falls and increasing ascent with moderate to strong elevated
instability could result in a few elevated supercells capable of
large hail and severe wind gusts late Saturday night and early
Sunday morning.

...Midwest/western Great Lakes...
Elevated thunderstorms will likely be ongoing Saturday morning
across southeast Wisconsin/northern Illinois on the nose of a
low-level jet. Isolated large hail/damaging wind gusts will be
possible with this morning activity. Some guidance suggests this
cluster maintains through the morning and becomes surface based as
it moves south across Indiana during the afternoon/evening. While
this is a possibility, the more likely scenario is weakening of
morning storms as the low-level jet weakens/veers. Additional
thunderstorms would then be possible during the afternoon along
remnant outflow/boundaries during the afternoon/evening. Regardless
of the exact evolution, moderate instability and moderate to strong
shear would support the potential for organized storms and at least
a localized threat for large hail/damaging wind gusts.

..Bentley.. 09/12/2025

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