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ACUS11 KWNS 290254
SWOMCD
SPC MCD 290254
MIZ000-INZ000-ILZ000-290400-

Mesoscale Discussion 1386
NWS Storm Prediction Center Norman OK
0954 PM CDT Tue Aug 28 2018

Areas affected...Portions of northern/central IL...northern IN...and southwestern Lower MI

Concerning...Severe Thunderstorm Watch 357...359...

Valid 290254Z - 290400Z

The severe weather threat for Severe Thunderstorm Watch 357, 359
continues.

SUMMARY...An isolated strong to locally damaging wind threat
continues across WW 357/359. Additional downstream watch issuance
into northern IN and southern Lower MI will probably not be needed.

DISCUSSION...Two separate clusters of thunderstorms are ongoing
across northern/central IL as of 0250Z. One of these clusters will
impact the Chicago metro area over the next hour or so, with mainly
a strong to locally damaging wind threat. A measured 59 mph wind
gust occurred at the Dupage Airport in IL at 0237Z. An increase in
radar reflectivity aloft has recently been noted with a cell
embedded within the southern portion of the line. With around 35-45
kt of effective bulk shear present, some updraft rotation may occur
with this embedded thunderstorm, with perhaps an isolated hail
threat.

Farther south, another cluster is moving eastward at 40-45 kt across west-central into central IL. Recent radar velocity signature from
KILX shows strong (50-60+ kt) inbound velocities around 5000 ft AGL.
These winds may not be fully reaching the surface given diurnal
cooling and at least some decoupling of the boundary layer. Still, a
moderately unstable airmass resides downstream of the ongoing
convection, and strong to severe winds should remain possible for
the next hour or two. The longer-term evolution of both of these
clusters remains somewhat uncertain, but there will probably be a
tendency for them to weaken with eastward extent as convective
inhibition continues to increase, and the composite outflow from
from both clusters sags southward into a weaker shear environment
with time. Current radar and mesoscale trends suggest the overall
severe threat will probably remain too isolated to justify
additional Severe Thunderstorm Watch issuance in northern IN and
southern Lower MI.

..Gleason.. 08/29/2018

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...IWX...GRR...LOT...ILX...LSX...DVN...

LAT...LON 39879113 40309110 41219065 41258995 41318921 41488872
42068848 42418827 42478709 42448584 42358528 41768506
41118575 40748680 40358793 39828951 39879113



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