Weather is complicated and hyper-local. The general public often lacks a basic understanding of weather evolution and people are generally bad at risk assessment. These facts combined make it really hard to provide general safety advice. It’s made even harder by the fact that if you give bad advice, you may be responsible for injury or death.
What to do when you’re in a car and a tornado is coming is perhaps the epitome of this issue. The National Weather Service office in Kansas City recently posted a scenario to its Facebook page. I saw some dismay expressed about how many people said they’d keep driving in that scenario. But here’s the kicker, I think that’s (conditionally) the right answer.
In the scenario you’re smack in the middle of a six mile stretch of interstate highway that’s expected to be impacted by a tornado in 15 minutes and you’re at an exit. The overpass is clearly the wrong answer. A very good answer would be to go to one of the gas stations or restaurants in the picture and seek shelter there. A car is about the worst place to be in a tornado, so why did I say “keep driving” is the right answer?
Let’s assume you’re traveling at 60 miles per hour. In three minutes, you’ve reached the edge of the warned area. The tornado won’t reach that area for another 12 minutes. Of course, there’s likely some error in the projection, but even if the forward motion is twice what was stated, you still have a cushion of over three minutes. If, in addition, the danger area is twice as large as stated, you still have 30 seconds. That’s cutting it too close, but we’re being really conservative here.
Now let’s look at all of the underlying assumptions that I made. First, I assume that you can safely travel at normal speed the necessary distance. This means no traffic, accidents, construction zones, or debris from earlier storms. In some places, you’d probably have sufficient visibility to make that determination, but certainly not in all places, and not in the picture shown. Second, I assume that you are just passing through. If you’re 10 minutes from home, it might be tempting to try to get there, but that eats into a lot of your safety buffer. Third, I assume you’re traveling south or that the main part of the supercell (another assumption) does not contain heavy rain or large hail that would slow you down or cause damage/injury on its own.
What would I do in that situation? It would depend on my familiarity with the area, my awareness of the storm type and evolution, and (most importantly), my ability to process it all quickly enough.
What should you do in that situation? See above. The best default answer is to seek shelter in one of the buildings off the exit, but that’s not always the best answer.