2018-05-12 EVENT: MO/IL/IN/OH

[Dan Robinson]

An east-west stationary front is shown by both NAM and GFS as settling in from the MO/IA border east into Ohio and even Pennsylvania as several ripples in the mostly zonal midlevels bring 30-50 knots of flow and effective shear values of 40+kts over the entire length of this boundary from the eastern Plains to the central Appalachians. Midlevel and low-level lapse rates are respectable, with backed surface winds likely along the various segments of the front. There are many examples of past Midwest tornado events that have occurred in this type of pattern.

Limiting factors include: 1.) a monster cap with 750mb temps as warm as 15c. Some runs are not breaking any convection out anywhere along the boundary. 2.) Westerly to west-northwesterly flow aloft in most areas will tend to make storms drift away from the boundary, though low-level SRH will be enhanced by this relative motion. Thus any regions with a southerly component of flow aloft (as in one of the ripples in the flow) would be favored to help a storm deviate on the boundary.

Target is unclear right now due to yet-to-be-resolved small scale waves in the mean upper flow and the exact position of the surface boundary. Right now Indiana is shown with a nice little embedded shortwave passing at 00z and turning flow southwesterly, but this is likely to change.

 

[Dan Robinson]

Models have backed off a little on the strength of the inversion, but still are not breaking out precip down on the boundary. The GFS forecast soundings along I-72 at 00z show it getting close, however. The environment just north of the front looks quite good for an Illinois sleeper tornado or two if a storm can get going. Watch visible satellite intently on Saturday morning/afternoon for clues on storm initiation.

 

[chrisbray]

I have been looking at this but the cap seems unbreakable. Not sure its worth a 2 hour drive south for me on something super conditional. Farther east into Ohio looks much more promising.

 

[chrisbray]

Example from latest NAM:

 

[Dan Robinson]

Yeah it's a long shot, but a slight improvement in upper support or H7 temps in the next 24 hours could make a huge difference. A realtime obs kind of day....