Mesoscale Discussion 1247
NWS Storm Prediction Center Norman OK
0102 PM CDT Thu Jun 13 2024
Areas affected...Much of Lower MI...Northern
IN...North-Central/Northeast IL
Concerning...Severe potential...Watch possible
Valid 131802Z - 132000Z
Probability of Watch Issuance...60 percent
SUMMARY...Thunderstorm coverage is expected to increase this
afternoon. Some large hail (up to 2" in diameter) and/or damaging
gusts are possible, and a watch will probably be needed.
DISCUSSION...Visible satellite imagery has shown increasingly
agitated cumulus from Lower MI southwestward into north-central IL,
well ahead of the cold front farther west that extends from central
Upper MI southwestward into west-central IA. This cumulus is
coincident with increasing mid to upper level cloudiness, suggesting
that it is likely in response to modestly increasing large-scale
ascent attendant to the low-amplitude shortwave trough beginning to
enter the Upper Great Lakes region. Some convective inhibition
currently remains present within the airmass across much of the
region, but gradual destabilization is anticipated throughout the
afternoon. Destabilization is expected first across Lower MI where
mid-level temperatures are cooler and greater large-scale ascent is
anticipated, before gradually moving westward with time as strong
diurnal heating continues. Thunderstorm initiation will likely
follow the same pattern, beginning over Lower MI and then expanding
westward with time. There is a chance that a brief thunderstorm or
two could develop across northern/northeastern IL first as
large-scale ascent combines within modest mesoscale ascent along the
pre-frontal trough.
Buoyancy will likely remain modest across Lower MI, with MLCAPE
likely remaining below 1500 J/kg. Stronger buoyancy is anticipated
across northern IN and north-central/northeast IL, where dewpoints
in the mid to upper 60s will help foster MLCAPE over 2000 J/kg.
Vertical shear is expected to be greatest over portions of northern
IL and northern IN as well, with effective bulk shear likely
reaching over 40-45 kt this afternoon. Consequently, the greatest
severe potential is anticipated across northern IL and northern IN,
with more isolated coverage expected across Lower MI. Large hail is
possible with initial development, but relatively high cloud bases
and steep low-level lapse rates suggest a relatively quick evolution
to outflow-dominant structures capable of damaging wind gusts. A
watch will probably be needed across portions of the area to cover
this severe potential.
..Mosier/Gleason.. 06/13/2024
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...DTX...APX...IWX...GRR...IND...LOT...ILX...DVN...
LAT...LON 40408796 40338929 40838984 41398996 42108923 42318826
42458737 42778669 43248639 43868597 44528530 44638427
43938351 43188334 42458360 41728441 40978570 40408796