SPC MD 444

MD 0444 CONCERNING SEVERE POTENTIAL...WATCH LIKELY FOR PORTIONS OF CENTRAL/SOUTHERN/WESTERN OHIO...NORTHERN KENTUCKY...CENTRAL AND SOUTHERN INDIANA...FAR SOUTHEAST ILLINOIS

Mesoscale Discussion 0444
NWS Storm Prediction Center Norman OK
0159 PM CDT Wed Apr 05 2017

Areas affected...Portions of central/southern/western
Ohio...northern Kentucky...central and southern Indiana...far
southeast Illinois

Concerning...Severe potential...Watch likely 

Valid 051859Z - 052130Z

Probability of Watch Issuance...80 percent

SUMMARY...The risk for severe thunderstorms with large hail,
damaging winds, and possibly tornadoes will spread northeastward and
east-northeastward across the region -- especially after 1930Z and
into the evening. Watch issuance will be likely for portions of the
Discussion area, though there is uncertainty regarding Watch type
(Severe Thunderstorm versus Tornado).

DISCUSSION...Deep surface low pressure (998 mb) analyzed between St.
Louis MO and Quincy IL will continue tracking east-northeastward
into a region of 2-hour pressure falls around 1-4 mb (maximized from
north-central IN into northern OH) during the next several hours. A
wavy warm-frontal zone, branching east of the low, will continue
developing northward into the region of ongoing pressure falls.
Lower to middle 50s surface dewpoints will spread northward -- as
far north as central IN to central/northern OH -- on the warm side
of the front into the evening.

Despite the limited boundary-layer moisture, relatively steep
midlevel lapse rates around 7.5-8.5 C/km -- sampled by the
Wilmington OH and Lincoln IL 18Z soundings -- will support MLCAPE
around 250-1000 J/kg. This should represent sufficient buoyancy for
ongoing developing cells in the warm sector closest to the surface
low in southern IL to intensify while tracking east-northeastward
and northeastward during the next several hours. The long hodograph
based on the Wilmington sounding suggests that ample convective
ventilation and deep shear will exist for sustained supercell
structures. Large hail -- possibly significantly severe -- will be
likely.

With effective SRH on the order of 200-300 m2/s2 -- highest values
expected near and just to the south of the surface low's track --
low-level mesocyclone development will be possible. Some tornado
potential will exist (aided by pre-existing vertical vorticity near
the surface low). However, the overall dearth of low-level moisture
will minimize low-level buoyancy, which could temper the strength of
low-level mesocyclones and tornado risk. Locally damaging wind gusts
may also occur, especially in association with amalgamating cold
pools.

..Cohen/Hart.. 04/05/2017

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

ATTN...WFO...CLE...ILN...LMK...IWX...IND...PAH...ILX...

LAT...LON   37768766 38108816 39708680 40508520 40718382 40288294
            39418292 38388423 37768766 

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