An anomalously strong late spring upper level trough will develop along the Eastern U.S. Coast by Friday. Two shortwaves, one ejecting out of the southern stream over California, will at least partially phase with a second shortwave that drops southward into the Great Lakes on Thursday. These will combine to strengthen a surface low that will traverse from Iowa eastward to the New Jersey Coast.
A two-day event is expected as severe convection will likely generate near the surface low Wednesday afternoon across Illinois and Indiana where the best forcing will exist, however further east across Ohio and West Virginia additional severe storms may develop with the aid of warm air advection and a mid level wind max in the northwest flow, during the afternoon. If discrete convection develops across Ohio/Western West Virginia on Wednesday afternoon there could be supercells and possibly strong tornadoes, given the favorable shear and other parameters. This is well ahead of the main forcing of the the surface low back to the west.
Intense convection is expected to develop across Illinois and Indiana and track eastward during the overnight hours. As the surface low deepens, warm air advection will continue to help destabilize the atmosphere near the warm front which is likely to be near Northern Ohio into Western Pennsylvania . A greater risk of significant tornadoes exist along this boundary. Just north of the warm front elevated convection may produce large hail and damaging winds.
Additional storms may develop further southward into Southern Missouri, Kentucky and Tennessee.
As the upper level shortwaves begin to phase, per the NAM. The surface low is expected to slow somewhat and should allow for some destabilzation across the eastern portion of Virginia, Maryland, Pennsylvania, New Jersey during the afternoon.
Wind fields will support supercells and possible tornadoes from Central Pennsylvania to New Jersey southward into the Carolinas . The best parameters for significant tornadoes on Thursday will exist near the warm front across Pennsylvania, Maryland, Delaware & into New Jersey.
*All of this is highly dependent on surface heating and interaction with prior convective outflow boundaries, none of which the models can properly resolve at this time range.
Below are some of the products used to create the outlook.
NAM Forecast Sounding for Columbus, OH Wednseday Evening.
Forecast Sounding for Baltimore, MD for Thursday Afternoon at 2PM EDT
NAM Sounding would support severe storms and possible tornadoes.