Tornado ‘hot spots’ are real

Weather

But there are still many questions about as to why they exist.

If you’ve lived in Alabama long enough, you’ve probably noticed that tornadoes tend to follow typical tracks. Some like to blame it on the river or a highway – or a mountain. We can’t answer all of the questions, but we do know there are some topographic influences that can make or break a storm like the one in Fultondale last night.

One of those typical hot spots is Sand Mountain in Northeast Alabama, and the code has been cracked: at least in part. Research done by Dr. Tony Lyza, a former UAH atmospheric science researcher now at Cooperative Institute for Mesoscale Meteorological Studies (CIMMS OU) showed enhanced tornado activity, especially within a few miles of the northern face of Sand Mountain (atop the plateau) because of a ‘standing wave‘ that enhanced low-level wind shear.

What about Jefferson County?

Three tornadoes in 10 years between Fultondale and Center Point. That’s significant:

  • An EF-4 ended northeast of Fultondale in 2011.
  • An EF-3 began between Fultondale and Center Point in 2012.
  • Monday night’s storm was at least EF-3 with 150 MPH winds, beginning near Fultondale and ending around Center Point (preliminary results).
The yellow track is the estimated path of the damage from Monday night’s storm

It turns out, there have been forty-four documented tornadoes within 10 miles of the Pawnee Heights neighborhood between Center Point and Fultondale from 1950 to 2017.

What causes that in the Birmingham metro area probably isn’t the same kind of thing that impacts Sand Mountain, but there’s probably something to that hilly terrain on the north side of Birmingham that can either enhance or kill a tornado’s spin depending upon the storm’s movement; in other words, the storm’s direction and speed coupled with the terrain may be a key.

The other key in the tornado Monday night was a thermal boundary (a very weak ‘front’) in the area. Storms riding along boundaries between rain-cooled, more stable air and steamy, untapped, muggy air can produce tornadoes when others would not.

What about North Alabama?

Pick a spot. You’ll hear about how the tornadoes almost always do this or that.

Let’s take Tanner for instance. Tanner is in southern Limestone County and has experienced some of the most intense tornadoes in Alabama history: a total of forty tornadoes from 1950 to 2017 within 10 miles of Tanner including two EF-5’s and two EF-4’s.

There aren’t any mountains around Tanner, so the terrain influence may not be quite as strong here, but we know something is going on in Limestone County (and northwest Madison County, too).

What is it? Can it be measured? And the most important question: can it be forecast?

There are four primary ‘scales’ of meteorology:

  • Microscale (smallest, less than 4-8 miles in extent, lasting less than an hour)
  • Mesoscale (medium scale, around 10 to 100 miles in extent, lasting hours to as long as a day)
  • Synoptic (large scale, events/systems that cover thousands of miles and several days)
  • Global (largest scale, big-time drivers like the jet stream, ocean currents, etc.)

Tornadoes happen on that smallest scale: microscale. Weather forecasts are based a little more on what we can actually see more clearly: the synoptic scale for the seven-day forecast and the mesoscale for tracking individual thunderstorms.

There’s not enough data from our observation networks and radars aren’t quite good enough at a distance to be able to always know which storm will produce a tornado and which one won’t do it.

A meteorologist’s least favorite phrase is “I don’t know.” It may not be what you want to hear, but that’s the honest answer when it comes to knowing if a storm will hit a county, city or neighborhood hours in advance. That’s why the watch and warning system works the way it does.

A Watch means it’s time to pay attention because severe storms are expected in the area soon.

A Warning means it’s time for action; a severe storm is happening now and it’s very close to you.

The best way to get a warning? NOAA Weather Radio. It’s tried and true, but you’ve got a great companion/back-up to that in your pocket: a phone that can use a location-based app to let you know that you are in danger.

You can also get up-to-date, location-based alerts wherever you are on Live Alert 19. Download it today for iOS and Android.

There’s never an ‘off’ season for severe weather in Alabama. We have our lulls now and then, but any month and any time of day can bring trouble. Be ready for the next time by preparing now!

Looking for the rest of the forecast? It’s always online at WHNT.com/Weather and in the “Daily Forecast” section on Live Alert 19!

-Jason
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