Thunderstorm threat increasing over northern Illinois.

Thunder clouds in DeKalb.

Mesoscale Discussion 0924
NWS Storm Prediction Center Norman OK
0205 PM CDT Sat Jun 01 2019

Scalloped area may require watch issuance.

Areas affected…South-central/southeast Wisconsin…far northern
Illinois

Concerning…Severe potential…Watch likely

Valid 011905Z – 012100Z

Probability of Watch Issuance…80 percent

SUMMARY…Thunderstorms have initiated in southwest Wisconsin with
an increase in coverage expected into more of southern Wisconsin and
northern Illinois. Damaging wind gusts and severe hail will be the
primary threats. A WW will likely be needed soon.

DISCUSSION…Thunderstorms have developed near the Dane/Iowa County,
WI border in the last hour. Activity has been weak thus far given
the ample amounts of cloud cover across much of southern Wisconsin.
Southeastern Wisconsin and northern Illinois have remained
relatively cloud free and have warmed to mid 70s F to low 80s F,
away from the influence of the lake breeze. Objective mesoanalysis
shows MLCAPE reaching 1000-1500 J/kg south of the warm frontal
boundary. Moderate mid-level flow of around 40 kts will foster
enough deep-layer shear for storm organization into multicells with
perhaps a few supercell structures as well. Greatest threat will
likely be damaging wind gusts, particularly where greatest
insolation/low-level lapse rates exists. Transient low-level
rotation will also be possible near the boundary where winds are
most backed. However, overall weak low-level flow and storm mode
issues will greatly limit tornado potential. A WW is likely to be
issued soon.

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