When is Tornado Season?

Apropos the recent tornadic activity here, a repost:

This story:

10 tornadoes confirmed in Ga., including one with winds topping 160 mph

Ten tornadoes, one packing winds of more than 160 mph, touched down in parts of Georgia on Wednesday, the National Weather Service said Friday.

The storms caused an estimated $25 million in insured losses, said John W. Oxendine, the state’s insurance commissioner.

“I spent some time surveying damage and talking to residents in Jasper, Putnam and Hancock Counties” on Friday, Oxendine said in statement. “I believe claims will easily reach $25 million. Actual losses are much higher when you consider things like infrastructure damage and uninsured losses.”

Reminds us that Tornado season is coming. Maybe it is already here in parts of the country, or maybe it is a bit early this year in the south. It is important to keep tornadoes in perspective. It would appear that for the last half century, the frequency of tornadoes in the US is rising, though this could be totally or in part because of increases in reporting. Warming climate should result in more tornadoes in areas where tornadoes already occur, or at least that is a reasonable assumption unless countervailing effects can be demonstrated.

So when is tornado season exactly?


Its complicated. The best way to answer this question is locally. Here in Minnesota the frequency of tornadoes starts to pick up in April, with the peak coming in June. In Georgia, where these reported tornadoes were, there is almost a bimodal season. They really can happen any time of the year in Georgia, but there is a major peak around mid february through about May, and another peak late in the year, around November, with this second peak being fairly weak.

The following is an animated GIF showing tornado activity from 1985 through 1989 over the course of a year.
i-f48787937cff3bbc7467ae1e4cb79e67-tw8589.gif

(If this starts to annoy you, just hit the “escape” key. That will stop any animated GIF in most browser windows. File under “computer tricks.”)

This is a fairly complicated pattern, but it is a pattern. Throughout the year, tornado activity spreads from south to north, as does thunderstorm activity. This sort of storm is most common in the middle, flatter parts of the country, but also, the energy that feeds these storms comes mainly from the Gulf of Mexico. This is the same sea-surface temperature (and over-sea moisture) effect that results in hurricanes which strike land in the US having a similar pattern. And, this is why it is logical to expect a global warming – tornado link.

NOAA has a great web site with the data referred to here, and more cool graphics, here.

And if you live in any of the lit up areas of this GIF, make sure your Weather Radio is working!!!

Comments

  1. #1 VampDuc
    August 20, 2009

    Oklahoma has ~5 climactic zones clashing directly on top of it. Every season is “tornado season”.

  2. #2 Alcari
    August 20, 2009

    “make sure youre Weather Radio is working!!!”

    tsk tsk Gred ;)

  3. #3 Alcari
    August 20, 2009

    Well, that would have been more impressive without me misspelling the name…

  4. #4 NewEnglandBob
    August 20, 2009

    When is tomato season?

    Well, you plant them after the last frost and that depends on where you live. Then they come out and you can start picking them in…..

    Oh! tornadoes…

    …never mind.