Thursday, January 26, 2012

How rare are Carolinas winter twisters?

When tornadoes struck two weeks ago in Burke, Caldwell and Rutherford counties, The Observer and some other sources reported that it was the first time in recent history that a twister struck those counties in January.

Certainly, mid-winter tornadoes are a rarity in the Carolinas, but with the possibility of more severe weather looming tonight, perhaps it's time to take a closer look at the history of "cool weather" twisters and the reason we're seeing them this year.

Pat Moore, who works at the National Weather Service's office in Greer, S.C., and is absolutely addicted to the science of meteorology, has spent the last few days studying records from the past 62 years and compiling a winter tornado history for the Carolinas.

Moore looked at tornadoes that struck in what meteorologists call the "cool season." That's meteorological winter -- Dec. 1 through Feb. 28 (or the 29th, this year).

His findings?

Several counties south of Charlotte, in areas where dew-point temperatures are more likely to rise in advance of approaching low pressure systems, have not recorded a tornado since 1950.

Here's what he found:

0 tornadoes since 1950: Cherokee, Chester, Lancaster and Union counties of South Carolina; Anson, Alexander, Catawba, Lincoln and Union counties of North Carolina.

1: Mecklenburg, Cabarrus and Cleveland. Add to that list, Burke, Caldwell and Rutherford, from the outbreak this month.

2: Iredell.

3: Gaston, Rowan and York.

The reason for the outbreaks of severe weather this month is fairly simple, really. Cold air has not penetrated into the South. For that matter, it really hasn't pushed into much of the United States at all.

Computer models show that most of the truly arctic air has been on the other side of the world -- over Russia, western Asia and eastern Europe -- for much of the winter.

A persistent low pressure system has sat over the Gulf of Alaska, and the counter-clockwise flow of air around that low has prevented arctic air from sliding down from the North Pole and moving into central Canada and the eastern United States.

With no cold air around, the Gulf of Mexico has stayed relatively warm. When low pressure systems move across the South, they are bringing a push of humid, relatively warm and unstable air into the Southeast. It's more of a spring-like pattern than what you'd expect from the middle of winter.

I've been writing since early December about the lack of cold air, and there are no signs of a change in the pattern for at least another 10 days. We might get a few brief (one- or two-day) outbreaks of chilly temperatures, but rapid warming will follow.

It's been a nightmare for snowplow operators and ski resort owners, although the Carolinas resorts have managed to make snow during the brief cold spells, and skiing conditions have been OK in recent weeks.


Anonymous said...

I just want some SNOW! Looks like we may not see any of it this winter. Bummer!

Anonymous said...

Where can I find statistics of MILD WINTERS? Someone @ 65 years old says he doesn't remember as mild a winter as 2011-12. When was last one?