Questions & Answers

a question related to the tornado of today's presentation.

a question related to the tornado of today's presentation.

by weiqing zhang -
Number of replies: 2

Hello Pierre,

I do have a question related to the tornado of today's presentation, but have no chance to ask after the presentation because of the technical problem I guess. In the presentation, two cases were compared, on in Gatineau and the other in Montreal. The one in Gatineau has higher each top but gave only hail and downpour; it is the one in Montreal with lower echo top that gave a F1 tornado. My question is “does that have something to do with the local topography, since the local effect can sometimes enhance the convection?”

Thanks a lot.

Weiqing

In reply to weiqing zhang

ther cellsRe: a question related to the tornado of today's presentation.

by Pierre Vaillancourt -

F0 and F1 tornadoes are very hard to predict as they can be associated with non-supercells or even TCUs like in the case of "gustnadoes" where the rotation is induced on the convergence line of two flows at low level.

In this case, both thunderstorms are along the edge of the mountains which could have help to increase the shear near the ground and increase the helicity for both. In fact, the stronger cell north of Gatineau is closer to a sharper cliff and the helicity should have been greater for it than over Mirabel.

There is one point I forgot to mention about the Mirabel cell and that is probably the trigger. If you look at the images in the PPT, you will see that the Mirabel thunderstorm is on the southwest edge of a convective line. This is often a very good place for the rear flank down draft to interfere with the low level inflow and the outflow of the otheres cells, especially when the topography enhance the shear. The Gatineau cell was more isolated.

In reply to Pierre Vaillancourt

Re: ther cellsRe: a question related to the tornado of today's presentation.

by weiqing zhang -

Thanks a lot for the detailed explanation.

Weiqing