Why a part of anvil splits at the edge?

Jul 8, 2004
SW Slovenia, Europe
Hi guys,

we had this sweet supercell last year here in Slovenia:



Maybe someone know why this happen:


Why a part of anvil secedes/splits at the edge? I've seen such forms maybe just a few times in last 10 years, usually this doesn't happen.
If you need some more data like sounding or anything, let me know, I will post if it helps.

Thanks for any help!

It's hard to tell without knowing whether that is the backsheared anvil or the downshear side. It looks backsheared and I too have seen this with backshearing anvils. My assumption would be that as the anvil spreads out, there is a induced horizontal rotation, like a horizontal vorticity tube if you will, induced by the vertical wind shear of the air flowing over the top of the storm, which is in an opposite direction of the direction the anvil is spreading out in. The differential in vertical windspeed induces what we call shear vorticity. On the downward moving side of this vorticity tube, the subsidence washes out the clouds in a narrow band.

I'll try to draw it out for you


Like I said, Just a guess based off of dynamic principles.... hell I could be totally wrong. :wink:
I was always under the impression that it was related to the updraft pulses. Often you'll see an intense cell of convection go up, hit the tropopause then spread out as an anvil. It continues to spread out (typically in every direction to some extent) then starts to diffuse near the edges. You then get a second pulse of convection which goes up and "reinforces" the anvil, thus causing the two tiered effect.

Just my guess....

Here's my example image...

EDIT: actually these two maybe dif. phenomena... I'd like to see some timelapse of both.

I think you are right Aaron in that they could be different phenomena. I've seen what you are describing as well. I think the sizeable difference in the clear area is what distinguishes them.

edit: also take not that my theory would only work in a backsheared anvil situation while the phenomenon you described could happen with buth the up and down shear sides of the storm.