Mesoscale Discussion 1489
NWS Storm Prediction Center Norman OK
0540 PM CDT Wed Aug 11 2021
Areas affected...Eastern IA...Southern WI...Northwest IL
Concerning...Tornado Watch 424...
Valid 112240Z - 120015Z
The severe weather threat for Tornado Watch 424 continues.
SUMMARY...Ongoing storms from eastern IA into southwest WI will
continue to pose a short-term severe threat. The eastward extent of
the threat this evening remains uncertain due to the impact of
earlier convection across southern WI/northern IL. Storm coverage is
being monitored for possible watch issuance across eastern IA.
DISCUSSION...At 2230Z, a few intense cells are ongoing from eastern
IA into southwest WI, within an environment characterized by large
CAPE and effective shear of 25-35 kt. The mature storms in this
region will continue to pose a short-term threat of locally damaging
wind, hail, and perhaps a tornado or two into the early evening as
they move eastward.=20
Downstream into south-central WI/northern IL, the impact of morning
convection is still evident, with relatively strong MLCINH
persisting per recent mesoanalyses and low-level stratus increasing
in recent visible imagery. Ongoing storms may tend to struggle with
time as they move eastward, especially given the relatively limited
large-scale ascent as the primary vorticity maxima move
northeastward away from the area. Low-level warm advection may
promote an increase in storm coverage later this evening, though
this scenario remains somewhat uncertain.=20
Meanwhile, across eastern IA, storm coverage remains uncertain into
this evening, though with a conditionally favorable environment in
place, watch issuance remains possible to the southwest of WW 424 if
additional intense thunderstorm development appears imminent.
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