611
ACUS02 KWNS 130552
SWODY2
SPC AC 130551

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1251 AM CDT Sat Sep 13 2025

Valid 141200Z - 151200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF
THE NORTHERN PLAINS...EXTENDING INTO THE SOUTHERN HIGH PLAINS...

...SUMMARY...
Isolated severe storms are possible across parts of the northern
Plains into the southern High Plains tomorrow (Sunday).

...Synopsis...
A negatively tilted upper trough will pivot northward across the
central/northern Plains, around broader cyclonic flow aloft, as a
second upper trough traverses the Pacific Northwest tomorrow
(Sunday). A surface low will develop and intensify while drifting
northward across the Dakotas through the forecast period.
Strengthening of the low will encourage the development of a
southerly low-level jet, which will result in both northward
moisture advection, and increased vertical wind shear, to support at
least isolated severe storms across the Plains.

...Great Plains States...
Widespread clouds and precipitation may be underway at the start of
the period (12Z Sunday) given the warm-air advection regime in place
ahead of the surface low. Through the day, some breaks in the cloud
cover will support adequate insolation to generate surface-based
buoyancy ahead of a confluence boundary. Surface temperatures may
rise into the 70s F, amid 60+ f dewpoints, yielding 1000-2000 J/kg
MLCAPE in spots. However, mid-level lapse rates are expected to be
modest at best (e.g. 6-7 C/km), with the aforementioned MLCAPE
constrained to tall, thin profiles. However, 20-40 kt southerly flow
at 850 mb (driven by the low-level jet), overspread by 40-50 kts of
south-southwesterly 500 mb flow, will yield elongated, mainly
straight hodographs across the central/northern Plains. Effective
bulk shear of 35-45 kts is possible from NE northward, with weaker
values, but relatively more curved hodographs possible farther south
into the southern High Plains.

By afternoon peak heating, the rejuvenation of warm-sector
convection ahead of the confluence band is likely, with scattered
multicells and perhaps supercells possible from the Dakotas to the
TX Panhandle. Storms will first develop across the northern Plains
by early afternoon, with gradual southward development likely by
early evening. Given modest lapse rates/thin CAPE profiles amid
straight hodographs, the severe threat appears relatively isolated,
with occasional severe gusts/hail the main threats. A tornado is
possible over the northern Plains if a supercell can become
sustained within the low-level jet axis and traverse a corridor of
locally stronger surface-based buoyancy. The severe threat should
gradually wane after dark, when surface-based buoyancy diminishes
with nocturnal cooling and increased MLCINH.

..Squitieri.. 09/13/2025

$$