26 October 2010

Autumn Twisters On The Prowl

Posted by Dan Satterfield

Numerical Weather Prediction model forecast. From NCAR/NOAA

When most folks think of tornadoes, they imagine a warm spring afternoon suddenly turning stormy. More often than not this is true but there are glaring exceptions. Last night was one and Tuesday will be another.

A powerful storm system has been winding up  in the Plains. Last night a band of storms from Texas to Alabama brought tornadoes and large hail. Here in North Alabama, I was up for much of the night watching radar.

What a tornado looks like on Doppler radar. Colours show winds toward and away from the radar. Image ctsy Penn State NEXRAD archive.

Large super-cell tornadoes are the easiest to spot and we had only one of those up in Tennessee. The ones you have to really watch for are the smaller more short lived twisters that are embedded in a squall line.

Around 4 AM CDT Monday morning, the Doppler radars indicated a strong circulation in the line over NE Alabama. The little town of Ider, near Fort Payne, was struck with a twister around 4:15.

The tornado looks to be an EF-1 or perhaps briefly an EF-2. An EF-1 tornado has winds of 32-50 meters per second (73-113 mph). That’s the equivalent of up to a category two hurricane on the Saffir-Simpson scale.

The Storm Prediction Center  (SPC) in Norman Oklahoma issues the tornado watches for all of the U.S. They’ve notified meteorologists like myself and at the local NWS forecast offices that they believe there is a rare “high risk” of tornadoes over Indiana and Ohio on Tuesday. A high risk is rare anytime.

It’s exceedingly rare in autumn.

SPC does only one thing. Forecast severe weather. Meteorologists like myself give high credibility to their forecasts.

The Enhanced Fujita Scale- courtesy of the Storm Prediction Center (NOAA)

There’s been  an amazing technological revolution in forecasting over the last 30 years. In the 1970’s most tornado watches had no reports of tornadoes. Now it is rare for a watch not to verify.

When I was an undergrad meteorology student, I worked on a project at Okla. University in 1980 called SESAME. That stands for Severe Environmental Storms and Mesoscale Experiment. It was a fancy name for trying to correlate what severe storms were doing with what the new Doppler radars were indicating.

I remember being laughed at by people who called it a waste of money. It was anything but.

Doppler radars cover most of the nation now and make it possible for forecasters to give incredibly accurate warnings. An accuracy I could not have imagined back in 1980.

At 4:15am Monday, the Doppler radar here in North Alabama showed a strong rotation and a tornado warning was issued. We had it on the air in less than 15 seconds from the time the NWS pushed the button. Unfortunately, most people in the little town of Ider were asleep.

The ones who has NOAA weather radios were awake because a loud alarm had gone off. If you live in area where severe weather is likely, you should have one of these radios. They only cost about 30$.

It might save your life one night.

Want to know what is really frustrating to meteorologists? Broadcasting a tornado warning, knowing that most people are asleep, and will never hear it.

Until it’s too late that is.

Be safe,