244
ACUS11 KWNS 171953
SWOMCD
SPC MCD 171953
IAZ000-NEZ000-SDZ000-172200-

Mesoscale Discussion 0459
NWS Storm Prediction Center Norman OK
0253 PM CDT Thu Apr 17 2025

Areas affected...parts of ern NE into wrn IA

Concerning...Severe potential...Watch likely

Valid 171953Z - 172200Z

Probability of Watch Issuance...80 percent

SUMMARY...The initiation of strong to severe thunderstorms,
including supercells posing a risk for large, potentially damaging,
hail may increase by 5-7 PM CDT, if not a bit earlier.  It is
possible that the potential for a tornado or two could increase
near/north and east of the Greater Omaha area later this evening.

DISCUSSION...Trailing the surface low, which is now migrating north
of the Redwood Falls MN vicinity, a surface cold front is
maintaining a southward advancement into/across the Sioux
Falls/Sioux City areas, Norfolk NE and the Grand
Island/Kearney/Hasting NE vicinities.  Substantive boundary-layer
warming and moistening (including surface dew points near 60F)
continues in a narrow corridor ahead of this feature, where
mixed-layer CAPE may continue to increase up to around 2000 J/kg
within the next few hours, beneath a warm and capping elevated
mixed-layer area.

Models continue to suggest that mid-level forcing for ascent
associated with a weak short wave perturbation may increasingly
contribute to subtle mid-level height falls and erosion of the
lower/mid-tropospheric inhibition as far south as the Lincoln and
Omaha NE vicinities by 22-00Z.  As this occurs, potential for the
initiation of thunderstorm activity will increase, both along and
ahead of the cold front.  Although there may be a tendency for
convection to become undercut by the front, convection allowing
model output suggests that forcing associated with pre-frontal warm
advection may maintain at least one or two sustained storms,
propagating to the right of the 30-40 kt west-southwesterly mean
flow.

As long as this occurs, it appears that the environment may become
conducive to supercells capable of produce swaths of large hail, at
least occasionally in excess of 2 inches in diameter.  Low-level
flow and shear are initially weak, but strengthening toward early
evening might result in an increase in potential for a tornado
near/north and east of Greater Omaha.

..Kerr/Smith.. 04/17/2025

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...DMX...FSD...OAX...GID...

LAT...LON   41179772 41769755 42469675 42579490 41059573 40719646
            40809718 41179772

MOST PROBABLE PEAK TORNADO INTENSITY...UP TO 95 MPH
MOST PROBABLE PEAK WIND GUST...65-80 MPH
MOST PROBABLE PEAK HAIL SIZE...2.00-3.50 IN