Valid 241630Z – 251200Z
…THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PORTIONS
OF IOWA…SOUTHEAST MINNESOTA…AND WESTERN WISCONSIN….
…SUMMARY…
Severe thunderstorms will threaten parts of the central Plains and
Midwest today. Large hail, damaging gusts and a few tornadoes are
possible.
…IA to WI…
A strong upper trough and associated midlevel jet will move into the
northern Plains today, with height falls and large-scale forcing
overspreading parts of MN/IA/WI/Upper MI. A surface cold front
extends from western MN into eastern SD, and will track eastward
into IA later today. This boundary will be the focus for afternoon
thunderstorm development. Visible satellite imagery shows strong
heating is occurring in this region. Dewpoints are only in the 50s
to lower 60s, but are forecast to climb into the mid/upper 60s by
mid-late afternoon as advection occurs from the southwest. This
will result in a corridor of strong instability across much of IA
into southeast MN and western WI. Initial storm mode will likely be
supercellular, given strong deep-layer vertical shear, relatively
steep midlevel lapse rates, and high CAPE values. Very large hail
will be main threat with these storms, although damaging winds and a
few tornadoes are possible. The main tornado threat appears to be
over parts of western/central WI, but is contingent on robust
low-level moisture return depicted in model guidance. Storms will
likely congeal into linear segments by early evening and spread
eastward into WI with a continued risk of damaging winds and a few
tornadoes.
…KS…
The aforementioned cold front extends southward into KS, where ample
low-level moisture and strong heating will be present today.
Large-scale forcing is much weaker this far south, but weak frontal
convergence and a weak cap will likely result in widely scattered
storms over central KS this afternoon. Sufficient vertical shear
suggests rotating storms are possible with a risk of large hail and
gusty winds. The primary severe risk with this activity should
diminish by mid-evening.
..Hart/Bentley.. 09/24/2019
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