Different structure

[Robert Edmonds]

I know there are the occasional tornadoes that can rotate the opposing direction than they're suppose to. My question is can this occur on a larger scale with storm structure? Usually you see the hook in the SW part of the storm, could it be in NE or NW? Also, would this be more likely to occur say in the southern hemisphere? Even if this so is it also possible to happen in the US? It was just something I was thinking about, cause it made me think how odd it would be if this was the case and we were chasing say in Australia.

 

[Chris Allington]

I know there are the occasional tornadoes that can rotate the opposing direction than they're suppose to. My question is can this occur on a larger scale with storm structure? Usually you see the hook in the SW part of the storm, could it be in NE or NW? Also, would this be more likely to occur say in the southern hemisphere? Even if this so is it also possible to happen in the US? It was just something I was thinking about, cause it made me think how odd it would be if this was the case and we were chasing say in Australia.

Tornadoes almost always rotate the opposite direction in the southern hemishpere but occasionally some can occur anticyclonicly in the US... most of the examples ive seen are right when a supercell slits and the rfd cuts in creating a cycloninc curculation on the right split and a anticycloninc on the left...

 

[Shane Adams]

Another way anticyclonic tornadoes can form in the northern hemisphere is when you get a "horseshoe" type rotation. These aren't neccesarily storm splits, but rather a situation where the anticyclonic half of a split horizontal rotation (updraft stretching into the vertical) becomes dominant, or at least equal (to the cyclonic side). Remember, when an updraft tilts horizontal rotation to the vertical, there are two sides on either flank of the upward motion; cyclonic on the forward side and anticyclonic on the back side.

A great example of this was the anticyclonic tornado we observed near Kiowa, KS on May 12, 2004. It was weak, but it lasted about 2-3 minutes, preceeding the main (cyclonic) tornado which developed a few minutes later from the cyclonicly-rotating half of the couplet.

 

[Thomas Loades]

This is indeed the case in the southern hemisphere; the supercell tends to be upside-down, with the updraft base/wall cloud in the NW corner of the cell.

Here we see one such supercell that produced no known tornadoes, but dropped giant hail over eastern Sydney, NSW, on April 14, 1999, doing A$1.4 billion damage.