Mesoscale Discussion 1110
NWS Storm Prediction Center Norman OK
1248 PM CDT Sat Jun 26 2021
Areas affected...Parts of western through central lower Michigan
Concerning...Tornado Watch 321...
Valid 261748Z - 261845Z
The severe weather threat for Tornado Watch 321 continues.
SUMMARY...Intensifying thunderstorms posing a risk for isolated
tornadoes and damaging downbursts are possible across interior
central and southern Lower Michigan by 4-5 PM EDT.
DISCUSSION...Slowly strengthening and upscale growing thunderstorm
activity has organized into a line across southern lower Michigan.=20
This will likely continue advecting within 30-40+ kt southwesterly
deep-layer mean ambient flow across the Lake Michigan shoreline
through much of southwestern and central Lower Michigan by 20-21Z.
This appears supported by large-scale forcing for ascent to the east
of a lower/mid-level low centered over Iowa, perhaps aided by a
remnant MCV now crossing southeastern Wisconsin, and coincides with strengthening low-level and deep-layer vertical shear. This
includes a northeastward migrating south-southwesterly 850 mb jet,
which may continue to strengthen to 40-50 kt as it propagates across
southern Lower Michigan by late afternoon.
Due to generally modest to weak lapse rates, boundary-layer CAPE is
still weak, but will continue to gradually increase with additional
insolation. This is expected to be sufficient to support=20
substantive further intensification of the approaching line as it
moves onshore and inland. Isolated discrete storm development may
also occur ahead of the line, in an environment becoming
increasingly conducive to strengthening low-level mesocyclones
posing a risk for strong downbursts and perhaps a couple of
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