Mesoscale Discussion 477

Issued

Apr 10, 2017, 3:25 PM CDT (20:25 UTC)

Expired

Apr 10, 2017, 5:30 PM CDT

In force

2 hr

Issued by

the Storm Prediction Center

The Chicago radar (KLOT), 120 km from the middle of the area, began a volume at 20:27 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

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715 
ACUS11 KWNS 102026
SWOMCD
SPC MCD 102025 
OHZ000-MIZ000-INZ000-ILZ000-WIZ000-MOZ000-102230-

Mesoscale Discussion 0477
NWS Storm Prediction Center Norman OK
0325 PM CDT Mon Apr 10 2017

Areas affected...Portions of IL...extreme east-central
MO...IN...southern WI...southwest Lower MI...southern Lake MI...far
western OH

Concerning...Severe Thunderstorm Watch 138...

Valid 102025Z - 102230Z

The severe weather threat for Severe Thunderstorm Watch 138
continues.

SUMMARY...The risk for severe thunderstorms continues across Watch
138. An isolated severe risk may extend farther south, though
additional watch issuance is unlikely.

DISCUSSION...Isolated to scattered thunderstorms continue to develop
near a front from far south-central WI southward to west-central IL
and into east-central MO. The greatest coverage of this activity
lies within western portions of Watch 138, in proximity to the
strongest deep ascent, and will continue tracking
east-northeastward.

Surface-based convection encountering the strongest buoyancy will
extend across northern parts of central IL east-northeastward into
northwest Indiana -- characterized by 1000-2000 J/kg of MLCAPE aided
by a narrow corridor of dewpoints around 60F ahead of the front
beneath 8.0-8.5 C/km midlevel lapse rates. Semi-discrete cells
evolving near and south-southwest of the Peoria area will ingest
this stronger buoyancy and likely be the most intense across the
Watch area -- from the general area around Peoria east-northeastward
toward the Pontiac area and farther east-northeast toward the far
south suburbs of Chicago and adjacent far northwest Indiana. With
effective shear around 45-55 kt, supercell structures will remain
possible. The Lincoln IL VAD wind profile indicates slight veering
of winds with height above the ground, though with ample low-level
speed shear, supporting around 200-250 m2/s2 of 0-1-km SRH. An
isolated tornado could occur with the most intense storms, though
large hail and damaging winds should be the primary risk. Otherwise,
the risk for severe hail and locally damaging winds will continue
spreading across Watch 138, with the severe risk diminishing west of
the front.

South of Watch 138 near the front, storm coverage should remain more
isolated owing to weaker deep ascent, though an isolated severe
hail/wind risk may evolve from the Saint Louis vicinity into
southern parts of central IL. Convective coverage is presently
forecast to remain too limited for additional watch issuance. Also
south of Watch 138, from east-central IL into central IN, a separate
quasi-linear band of convection is evolving, and will continue
developing eastward/northeastward during the next several hours.
This activity will be supported by gradually moistening inflow
(surface dewpoints rising into the lower 50s) yielding weak
buoyancy. Effective shear around 30-45 kt, combined with 30-40 kt of
flow around 1-2 km above ground, may support semi-organized
convective structures capable of locally damaging wind gusts. Weak
buoyancy should minimize severe coverage such that additional watch
issuance is unlikely.

..Cohen.. 04/10/2017

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

ATTN...WFO...ILN...IWX...GRR...IND...PAH...LOT...ILX...MKX...
LSX...DVN...

LAT...LON   39018679 38468919 38449027 38879066 40719021 42468945
            43128891 43368682 42718551 41338464 40368468 39668537
            39018679

Mesoscale Discussions in Illinois, 2017Mesoscale Discussions in Indiana, 2017Mesoscale Discussions in Michigan, 2017Every mesoscale discussion in 2017

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.