Tornado Drought Officially Over
May 21, 2013
I’m declaring the tornado drought officially over.
Monday’s horrifying events in Oklahoma are still being sorted out. Standard disclaimers apply, “No particular weather event …” etc
I have a statement from Dr. Kevin Trenberth of the Natonal Center for Atmospheric Research by email:
Of course tornadoes are very much a weather phenomenon. They come from certain thunderstorms, usually super-cell thunderstorms that are in a wind shear environment that promotes rotation. The main climate change connection is via the basic instability
of the low level air that creates the convection and thunderstorms in the first place.
Warmer and moister conditions are the key for unstable air.
The climate change effect is probably only a 5 to 10% effect in terms of the instability and subsequent rainfall, but it translates into up to a 32% effect in terms of damage.
(It is highly nonlinear).
So there is a chain of events and climate change mainly affects the first link: the basic buoyancy of the air is increased. Whether that translates into a super-cell storm and one with a tornado is largely chance weather.
Below: Damage in Moore, Oklahoma, from the air.