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Latest SPC Mesoscale discussion hints at possible severe thunderstorm watch into portions of northwest and north central Illinois later this evening
Mesoscale Discussion 0722
NWS Storm Prediction Center Norman OK
0719 PM CDT Mon May 15 2017
Areas affected...Northern Iowa...southern Wisconsin...and northern
Concerning...Severe Thunderstorm Watch 214...
Valid 160019Z - 160115Z
The severe weather threat for Severe Thunderstorm Watch 214
SUMMARY...Ongoing severe hail/wind threat should reach the eastern
portions of WW 214 around 01-02Z. A downstream severe thunderstorm
watch will be needed around or before 01Z. Additional redevelopment
may occur in western portions of the watch that would pose a hail
DISCUSSION...Broken linear segments have evolved over north-central
and northeastern Iowa, with a series of significant hail and wind
reports primarily owing to hybrid bowing/supercell structures in the
region. The convection is propagating eastward at around 30-35
knots along a remnant outflow/stationary boundary, with a moderately
unstable pre-convective airmass and sufficient vertical wind shear
favoring continued organization and a severe threat (potentially
significant in localized areas) extending east into southern
Wisconsin and northern Illinois. A downstream severe thunderstorm
watch is being considered in these areas and will be coordinated
soon with affected local forecast offices.
Farther west, short-term/high-resolution models continue to suggest
redevelopment of convection in southern Minnesota and northern Iowa
on the nose of a strengthening low-level jet. Steep mid-level lapse
rates will aid in fostering a severe hail threat with this activity
when it develops and some potential exists for this activity to
develop in western portions of WW 214. For this reason, the severe
threat across the entirety of the WW continues.