Damage surveys in the wake of Sunday's tornado outbreak across the southern United States have revealed an unusual feature: The deadly EF-4 tornado that swept through eastern Alabama was followed, almost exactly, by a second long-track tornado, less than an hour later.
The tracks of the two storms are less than a mile apart in some spots, with the stronger storm rolling through the region at about 2 pm Sunday afternoon (local time), and the second following close on its heels, coming close to partially overlapping the initial twister's path.
That made conditions especially harrowing for first responders, who were already on their way into the region in the wake of the first storm while the second was already bearing down on the region.
It's impossible to quantify the odds on this kind of an 'instant replay' track, but generally speaking once a major storm moves through an area, the nature of the local atmosphere there is changed.
If you think of the particular humidity, temperature, and wind dynamic conditions that are in place to trigger a supercell thunderstorm that then goes on to produce a tornado, once the supercell has moved through, those conditions are different; moisture is reduced, winds shift, and so forth. The overall effect is, generally speaking, to stabilize the atmosphere in the wake of the storm. It's worth noting that, while the second tornado did take a very similar track, it first touched down well to the west of the initial EF-4-producing storm.
The earlier, stronger of the two tornadoes is the one responsible for all 23 fatalities resulting from Sunday's outbreak, and is estimated to have had peak winds near 275 km/h.