Sometimes in forecasting tornadoes, you can get everything technically right, and yet it all goes horribly wrong.
Three days before the killer Alabama tornado struck, government severe-storm meteorologists cautioned that conditions could be ripe for twisters in the Southeast on Sunday. Then, an hour before the tragedy, they warned that a strong tornado could occur in two particular Alabama counties within 30 to 60 minutes.
And that’s what happened.
Yet 23 people died.
To a meteorologist, the forecast was the equivalent of a hole-in-one in golf or a slam dunk, but with so many people killed, “was it a success or a failure or both?” asked Colorado State University meteorology professor Russ Schumacher.
Forecasters “painted a pretty clear picture that something bad was going to happen,” Schumacher said, and “there’s certainly success in that. On the other hand, we don’t like to see entire communities to be turned upside-down like this. So there’s more to be done.”
Predicting with any precision where a tornado is going to go is still beyond the limits of meteorology, which is why warnings went out for a large two-county area when a tornado might be only half a mile wide. And getting people to listen and take precautions is another matter altogether.
Forecasting tornadoes combines the hard physics of meteorology, the softer human factors of social science and more than a dash of chaos.
At the National Oceanic and Atmospheric Administration’s Storm Prediction Center in Norman, Oklahoma, forecasters look for certain ingredients that can make a tornado. These include warm moist air coming from the south and stormy weather chugging from the west that can bring instability. That’s when you can get supercells, which is where tornadoes come from.
But maybe only 10 to 20 percent of supercells spawn tornadoes, said prediction center forecast operations chief Bill Bunting. There are other factors at work, including erratic wind behavior known as wind shear, the amount of cold air present, even the size of the rain droplets, meteorologists said. And then there are the unknown factors at play.
Given all that, the best meteorologists can do is say seven to eight days out — four to five is more usual — when conditions will be ripe for tornadoes, Bunting said. And even that doesn’t mean they will happen. And certainly not over all of the large area that meteorologists give in their several-day-out alerts.