ACUS11 KWNS 272051
SWOMCD
SPC MCD 272050=20
INZ000-MIZ000-ILZ000-WIZ000-IAZ000-272245-

Mesoscale Discussion 0163
NWS Storm Prediction Center Norman OK
0250 PM CST Tue Feb 27 2024

Areas affected...Northern IL and far northwest IN

Concerning...Severe potential...Tornado Watch likely=20

Valid 272050Z - 272245Z

Probability of Watch Issuance...80 percent

SUMMARY...A few supercells are expected to develop over parts of
northwest Illinois and then spread east-northeast across northern
Illinois into far northwest Indiana through early evening. Very
large hail to around baseball size will be the primary initial
threat. A conditional strong tornado scenario may develop later over
northeast Illinois into far northwest Indiana.

DISCUSSION...20Z subjective surface analysis placed a 990-mb cyclone
near the Quad Cities along a pronounced cold front sweeping
southeast across the Upper MS to Lower MO Valleys. A bent-back plume
of relatively richer surface dew points from the mid to upper 50s
lies immediately ahead of this wave, along the northwest periphery
of the broader warm-moist sector across the OH Valley and lower
Midwest. Within the exit region of an intense mid-level jet shifting
east from the southern Great Plains to the Lower OH Valley,
continued ascent should yield sufficient weakening of MLCIN during
the 22-23Z time frame. Initial storm development is most likely in
the immediate vicinity of the surface low.

The environment will be favorable for discrete supercells forming
despite initially modest low-level shear. Amid very steep mid-level
lapse rates, large to very large hail production is expected, with
peak intensity around 2 to 3.5 inches possible. The primary
uncertainty is with how convection evolves downstream given the
relatively narrow warm/moist sector where storms develop. There
should be a tendency for convection to spread into a drier boundary
layer towards the WI border. It is plausible, within a scenario
highlighted by various 12Z MPAS members and occasionally by later WoFS/RRFS/HRRR runs, that a longer-tracked supercell or two may
develop into the broader warm-moist sector across northeast IL into
far northwest IN. Low-level shear within this region will be
increasing towards and after dusk, which will conditionally support
potential for a strong tornado into the EF2-EF3 range (peak
estimated gusts around 120 to 150 mph).

..Grams/Hart.. 02/27/2024

...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!9gJZU6vsdWjCbgGntJhS9wmD8oMBtDLVv56QYTk9_rcwLQJSOGooIMY26VCx4URX6LDLBGr85= USsPd7aoB16S1yaQo4$ for graphic product...

ATTN...WFO...IWX...IND...LOT...ILX...MKX...DVN...

LAT...LON 41339107 41889019 42428914 42648804 42478749 41728666
41188637 40588664 40008714 40078770 40758927 40549065
41339107=20


=3D =3D =3D
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