Why Do Some Tornados Rotate Clockwise

[Patrick Ware]

What atmospheric dynamics force a tornado/funnel cloud to rotate clockwise?
What percentage of tornados in the Northern hemisphere rotate clockwise?
What is the chaser jargon for these different tornados?

 

[Jeff Snyder]

Anticyclonic tornadoes seem to be associated with anticyclonic mesocyclones (go figure, huh) or rotation more shallow and shortlived than can be deemed a mesocyclone. Given the nature of the westerly flow aloft over the U.S., the best instability days tends to be associated with low-level warm air advection, which is signified by a veering wind profile. This type of wind profile favors cyclonic mesocyclones/supercells. There are conditions where anticyclonic supercells are favored in cases when the wind profile is backing with height, conditions with a backing vertical wind profile tend not to be juxtaposed with higher instabiility (backing profile -> cold air advection -> not good for instability)... Now, to the south of the rear-flank downdraft in a supercell, there may be an opportunity for anticyclonic rotation to develop (such was the case May 29th in central OK), which may produce an anticyclonic tornado. This rotation tends to be relatively shallow since it isn't necessarily associated with a prolonged updraft, which means that anticyclonic tornadoes tend to be small and relatively short-lived. Of course, this is pertaining to supercells, but there could be anticyclonic tornadoes produced by mutlicells, likely courtesy of complex boundary interactions which may temporarily produce an environment favorable for anticyclonic tornadoes...

 

[Chris Nuttall]

Sometimes you can also get anticyclonic tornadoes out of splitting supercells. The right-moving (right-split) storm will have cyclonic rotation, while the left-mover (left-split) will have anticyclonic rotation. If the left-mover can sustain long enough and conditions are just right, sometimes they can drop tornadoes...which will rotate anticyclonically.

 

[Jim Bishop]

Some landspout tornadoes rotate clockwise. They can rotate in either direction since they are not associated with a mesocyclone circulation. They form near mesoscale baroclinic zones where the air has a tendency for horizontal rotation. That meets an updraft and boom, tornado. Since the tornadic rotation is not predetermined by the storm rotation (i.e. a supercell) the landspout could rotate cyclonically or anticyclonically.