Analysis of a Complex Mesovortex Evolution during the Second 30 June - 1 July 2014 Derecho Event

A tornadic quasi-linear convective system (QLCS) impacted northern Illinois and northern Indiana on 30 June - 1 July 2014. The event produced 29 confirmed tornadoes and numerous straight-line wind damage reports. A mesovortex formed in northeastern Illinois and then tracked east, splitting into two subvortices. The subvortices produced 14 of the 29 confirmed tornadoes and areas of straight-line wind damage that reached near-EF2 intensity. The northern subvortex produced up to 3 simultaneous tornadoes in close proximity to each other. In this presentation, characteristics of the subvortices, including intensity, size, and depth, were examined using a single-Doppler analysis approach. Examples of analyzed properties of the two subvortices include:

1) The northern subvortex measured nearly 9 km deep at maximum depth, which scales closely with a depth associated with supercell mesocyclones more so than QLCS mesovortices, while the southern subvortex was only 3 to 4 km deep, more typical of a QLCS mesovortex;

2) When the original mesovortex split into two subvortices, they were equal in size and strength; however, the northern subvortex eventually became dominant, with the southern vortex rotating around it;

3) The northern subvortex maintained a greater diameter than the southern subvortex for much of its existence; and

4) Low-level rotational velocity tended to be much higher in the northern subvortex than the southern subvortex.

In addition to these properties, damage surveys will be related to radar observations from the single-Doppler analysis. Observations from this event will be related to past research studies on QLCS mesovortices.