121
ACUS01 KWNS 200527
SWODY1
SPC AC 200526

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1226 AM CDT Fri Sep 20 2024

Valid 201200Z - 211200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM SOUTHWEST
LOWER MICHIGAN INTO PARTS OF INDIANA...ILLINOIS...AND SOUTHEAST
MISSOURI...AND OVER PARTS OF THE CENTRAL PLAINS...

...SUMMARY...
Isolated strong to severe thunderstorms are possible during the late
afternoon over parts of Illinois, Indiana, and southwest Lower
Michigan. Isolated strong to severe storms are also possible across
parts of the south-central Plains.

...Synopsis...
A leading shortwave trough will weaken as it moves across the upper
Great Lakes today, while a secondary and stronger system moves into
MT and the northern Plains late. An upper high will hold over the
southern Plains, which will aid a strengthening midlevel height
gradient over the central and northern Plains as the wave approaches
from the northwest. Meanwhile, a deep upper low will affect southern
CA and move into AZ through Saturday morning.

At the surface, a trough will develop over the northern High Plains
late in the day, with high pressure over the eastern states. A
weak/residual boundary will extend roughly from Lake MI into central
IL, MO, and toward I-70 in KS, with a moist air mass to the south.
Mid to upper 60s F dewpoints will return north late this evening and
overnight as southerly winds around 850 mb increase to over 40 kt.
Otherwise, a cold front associated with the MT disturbance will push
across the Dakotas and into central NE overnight and through 12Z
Saturday.

...Western Lower MI into IN and IL...
Daytime heating of a moist low-level air mass will yield a
moderately unstable and uncapped air mass near the weak surface
boundary. Scattered thunderstorms are anticipated from western Lower
MI southwestward into southern MO as a result. However, forecast
soundings indicate poor midlevel lapse rates along with substantial
midlevel dry air, which may diminish severity somewhat. That said,
locally strong gusts will be possible, and perhaps small to marginal
hail.

...Central Plains...
Strong heating and southwest surface winds will lead to a plume of
steep low-level lapse rates from the TX Panhandle toward the KS/OK
border this afternoon. Meanwhile, higher dewpoints will remain near
a stalled front over KS, which will support high-based storms
initially over northeast NM across the Panhandles and into southwest
KS. Given the very deep mixed layers, a few strong to severe gusts
may occur. With time, outflow may yield downstream development with
more robust cores and perhaps marginal hail across south-central KS.

During the late evening, the returning boundary and associated
theta-e advection may support a rash of storms from near the NE/KS
border, with veering 850 mb winds over time redirecting said
advection and lift eastward across the KC Metro. Strong wind gusts
appear to be the main risk with such activity.

..Jewell/Thornton.. 09/20/2024

$$