Do you recall learning about tornadoes in elementary school? I do. In Mississippi, we were taught the basics: tornadic storms form when warm, moist air from the Gulf of Mexico clashes with cold, dry air crossing the Rockies. That information was pretty accurate when my whole world consisted of the town in which I lived. Knowing what I know now, it wasn’t wrong, but it wasn’t totally right either.
Tornadoes can occur anywhere, which means the Gulf of Mexico and the Rocky Mountains are not required for their formation. What is required is a battle zone between two conflicting air masses. Warm, moist air and cooler, drier air are definitely needed. The bigger the difference between them, the stronger the frontal system.
Rotation in the atmosphere is also needed to spin up a twister. Not every strong cold front will spawn tornadic storms. All the right pieces have to be in place.
We’re still in the process of learning exactly why some storms with all the right ingredients will produce tornadoes and some will not. For the longest time, we thought they all reached down from the base of a supercell cloud. Last year, a study discerned that at least some tornadoes may form from the ground up. Each year brings new data and hopefully a better understanding of why twisters happen.
The good news is with each little increase in knowledge, we are getting better at forecasting potential severe weather days. It used to be that we couldn’t be very accurate more than three days in advance. Now, we can see the potential for severe weather up to eight days out. As with any forecast, the closer we get to the day of the storm, the more precise we can be about when and where the battle zone will be.
Yesterday, while looking at the Storm Prediction Center website, I noted there was already a region highlighted with a 15% risk for severe weather five days out – Saturday morning through Sunday morning. The map wasn’t a surprise to me after having made the forecast for the weekend. I could see the setup for a strong frontal system to cross the Midwest and the south during that period. Seeing that risk highlighted was actually a small point of pride in our science. We’re getting better at this!
Today, the five-day outlook is for Sunday morning through Monday morning and shows a risk across the southeast. It makes sense given the forecasted movement of the same frontal system.
So, what does a 15% risk of severe weather across an area mean? It means that there is a 15% chance that a severe thunderstorm will occur within 25 miles of any point. So, at any one point, the risk is slight, but across a region that covers several states, it means someone is probably going to experience severe weather – possibly many someones.
Anyone within that highlighted area needs to be situationally aware with respect to changing weather conditions during that time period. Situational awareness means knowing where the storms are in relation to where you are. It also means thinking ahead about where you would take shelter if a severe storm, or worse – a tornado – hits your location.
Think ahead because in the middle of a crisis, there isn’t always time to think.
Whether we have five days of advanced notice or just 15 minutes to get to safety, being weather aware and situationally aware can make a world of difference when it comes to surviving the worst.