ACUS01 KWNS 122002
SWODY1
SPC AC 122000

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0300 PM CDT Fri Sep 12 2025

Valid 122000Z - 131200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE FOUR
CORNERS VICINITY AND ALSO ACROSS THE NORTHERN HIGH PLAINS...

...SUMMARY...
Isolated severe storms remain possible this afternoon across the
Four Corners area and central Rockies, with an increasing risk for
severe storms into late afternoon and tonight across the northern Plains.

...Four Corners vicinity into the Southwest...
The Slight Risk has been expanded westward into parts of
southeast/east-central UT, where favorable deep-layer shear and
modest but sufficient instability remains in place this afternoon.
Occasional small supercells will continue to be possible, with a
threat of hail and localized strong/severe gusts. See MCD 2066 for
more details.

The Marginal Risk has been expanded slightly westward across
southeast AZ, based on trends on visible satellite. The 18Z TUS
depicted a favorable conditional environment for severe storms, with
moderate MLCAPE and deep-layer shear. While the threat should
generally remain rather isolated, a supercell or two will be
possible, with an attendant threat of hail and localized severe
gusts. See MCD 2065 for more information.

...Northern High Plains vicinity...
Only modest adjustments have been made to the Marginal Risk across
the northern High Plains vicinity, with no changes to the Slight
Risk. An isolated threat for hail and strong/severe gusts may
develop later this afternoon, with some increase in coverage of the
severe threat expected into this evening. See MCD 2067 and the
previous discussion below for more details.

...East-central MN into northwest WI...
Much of the Marginal Risk across MN and northwest WI has been
removed. An earlier cluster of storms has generally weakened this
afternoon across east-central MN, though modestly steep midlevel
lapse rates and relatively favorable effective shear could still
support a threat for small to near-severe hail and locally gusty
winds as these storms move into northwest WI. Additional elevated
convection may develop later tonight across the same general region,
but severe potential with the later storms appears limited at this time.

..Dean.. 09/12/2025

.PREV DISCUSSION... /ISSUED 1139 AM CDT Fri Sep 12 2025/

...Four Corners Region/central Rockies...
Ahead of the prominent upper trough centered over the Great Basin
and Lower Colorado River Valley, a lead mid-level impulse and
related height falls and a strengthening of cyclonic flow aloft will
influence the region. Cooling mid-level temperatures and a modestly
warming boundary layer will further steepen lapse rates diurnally,
with strong to severe storms expected to further develop into the
afternoon. Relatively strong flow aloft with 40+ kt effective shear
will support some supercell structures, with a related enhanced
potential for severe hail, aside from locally gusty thunderstorm
winds. More severe-favorable ingredients and a somewhat higher
potential for severe storms appears to exist across the Four Corners
vicinity including northwest New Mexico across western Colorado
through the afternoon.

...Northern Plains including Eastern Montana/western Dakotas...
Thunderstorm development/intensification is expected by late
afternoon, initially on an isolated basis across central/eastern
portions of Montana and Wyoming. Cooling mid-level temperatures and
surface dew points in the 50s F will contribute to 500-1000 J/kg
MLCAPE. Southwesterly deep-layer shear averaging 20-35 kt will be
favorable for isolated storms with hail potential. Storm coverage
should steadily increase into the evening toward the western
Dakotas, aided by the arriving influence of greater forcing for
ascent as located over the central Rockies early today. Hail
potential will become more common this evening, with localized
severe wind potential also modestly increasing. Strong/locally
severe storms will potentially persist overnight across the western
and central Dakotas.

...Northern/central Minnesota to northwest Wisconsin...
Very isolated elevated severe storms, with hail as the most probable
hazard, may continue east-southeastward today, semi-focused by
elevated moisture transport well to the north of a warm front.

$$
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