Storm Structure 101 DVD...Donut Hole??

[MG Jennings]

I was watching Storm Structure 101 and Mike(?) references the "donut hole" in one of the storms. I have seen this multiple times in storms...What exactly is the donut hole, what causes it and does it have any significance regarding storm structure?

thanks

 

[Skip Talbot]

Its a rear flanking downdraft clear slot. In some instances, it forms a clean hole in the updraft base, but usually it cuts a big notch out of the back end of the updraft base making it into more of a horseshoe shape. Since its an RFD clear slot it can be very influential in tornadogenesis.

 

[Skip Talbot]

The above shot is from an HP that didn't produce. Here's a good example of one that did on April 9 last year near Mapleton, IA:

That RFD was drier, and formed a nice clear hole in the updraft base and was associated with some hybrid tornado/gustnado/outflow activity. This preceded the Mapleton F3 by about 20-30 minutes I believe, which was associated with some wetter RFD surges.

 

[MG Jennings]

Thank you very much Skip