Strong thunderstorms will be possible from the southern Plains into the Ohio and Tennessee Valleys during the afternoon into the overnight hours. Isolated large hail and damaging winds may be possible with the strongest storms.
A seasonably strong/cold midlevel low will persist across Ontario,with an attendant larger-scale trough persisting across much of theeastern United States. A potent midlevel shortwave trough will beacross the Upper Great Lakes at the start of the period and willquickly rotate around the upper low into Quebec through the period.In its wake a midlevel ribbon of higher vorticity will be leftbehind from Iowa northeast across Michigan. Upstream from this, themidlevel height field will begin to respond to another shortwavetrough rotating around the Ontario low.
At the surface, a surface low will quickly lift northeast fromnorthern Michigan through Ontario and into Quebec through theforecast period. A cold from will extend southwest from this low andwill push south and east as the surface low lifts northeast.Although somewhat diffuse initially, the temperature gradient acrossthe cold front will rapidly strengthen through the day.
Diurnal heating should allow afternoon temperatures to warm into the80Fs and 90Fs across the region. Given surface dewpoint temperaturesin the mid 60Fs perhaps as far north as southern Ohio, this heatingwill result in most-unstable CAPE values in excess of 2000 J/kgacross the area. The region will also be on the periphery of thestronger midlevel flow, yield effective shear of around 40 knots.
Thunderstorms should develop by late afternoon in response toincreasing large-scale ascent associated with both differentialvorticity advection and frontal circulations. Given the degree ofinstability and effective layer shear, initial thunderstorms mayexhibit supercellular structures. However, given thetemperature-dewpoint spreads on the order of 20F+ the expectation isthat thunderstorms should tend to favor upscale growth toward linearsegments. As such, thunderstorms may initially pose a hail threat,especially across western Kentucky and Tennessee, but shouldtransition to more of a wind threat with eastward extent.
Across portions of Kentucky and southern Ohio, a short-window,conditional tornado threat may evolve as thunderstorms develop inthe vicinity of the surface boundary. As thunderstorms interact withor cross over the boundary, strong northeasterly surface winds willenlarge low-level hodographs supporting at least some tornadothreat.
The surface cold front across the region is expected to strengthenduring the day as it slowly moves south. During the evening into theovernight hours, strong warm-air advection on the nose of astrengthening low-level jet may support thunderstorm development onthe cool side of the cold front. Despite surface temperatures in the60Fs and low 70Fs, steep mid-level lapse rates atop the coldersurface layer may support isolated large hail.