509
ACUS01 KWNS 021959
SWODY1
SPC AC 021958

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0258 PM CDT Tue Sep 02 2025

Valid 022000Z - 031200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
EASTERN SOUTH DAKOTA INTO SOUTHERN/CENTRAL MINNESOTA AND FAR
NORTHWESTERN WISCONSIN...

...SUMMARY...
Thunderstorms capable of producing isolated severe wind gusts and
marginally severe hail will be possible this afternoon and evening
across parts of the northern Plains and Upper Midwest.

...20Z Update...
No changes were made to the ongoing forecast. Strong to marginally
severe storms still appear possible along a cold front in the
northern Plains/Upper Midwest. See the previous discussion for
additional details.

..Wendt.. 09/02/2025

.PREV DISCUSSION... /ISSUED 1125 AM CDT Tue Sep 02 2025/

...Northern Plains/Upper Midwest...
An upper trough over central Canada late this morning will dig
southeastward towards the Upper Midwest/Lake Superior vicinity
through the period. Showers and weak thunderstorms are ongoing over
parts of central MN, aided by a remnant MCV over northern MN. This
activity is forecast to further weaken this afternoon, with a
residual outflow boundary arcing from southern MN west-northwestward
towards the SD/MN border by mid afternoon. A cold front over ND will
continue to advance southeastward into an adequately moist low-level
airmass, with surface dewpoints generally in the lower to mid 60s.
Filtered daytime heating away from this morning`s convective cloud
debris, along with modestly steepened mid-level lapse rates
(reference 12Z ABR sounding), should aid in weak to locally moderate
instability (MLCAPE around 1000-2000 J/kg) developing ahead of the
front by mid to late afternoon.

Latest model guidance remains consistent in showing isolated to
scattered thunderstorms developing across roughly the eastern third
of SD into central MN this afternoon along/near the cold front.
There is considerable uncertainty regarding the degree of
instability that will develop and related thunderstorm intensity
given the widespread cloud cover in south-central MN. The stronger
mid/upper-level flow associated with the upper trough over Canada
will likely lag behind the surface front to some extent. This should
limit effective bulk shear magnitudes (up to 20-30 kt). Even so,
modestly organized multicells associated with isolated severe wind
gusts and marginally severe hail appear possible, before this
activity eventually subsides this evening with the loss of daytime
heating. The Marginal Risk has been adjusted to account for the
latest observational/short-term guidance trends.

...Lower Colorado River Valley...
Compared to yesterday, modestly enhanced mid-level flow should trend
more south-southeasterly today as a weak shortwave trough lifts
northward from Baja California into the lower CO River Valley.
Associated/ongoing showers and thunderstorms across southern CA
should generally remain sub-severe through the morning as they track
northwestward. In the wake of this activity, there is a fair amount
of uncertainty regarding destabilization potential given scattered
to widespread cloudiness over much of the lower CO River Valley.
Wherever cloud breaks and heating can occur, steepening low-level
lapse rates may support strong/gusty winds with any convection that
can develop. Still, the potential for a focused area of severe gusts
appears too low to include any probabilities at this time.

$$