Severe thunderstorms include many threats, perhaps the most dangerous being tornadoes, but what goes into creating these beautiful but destructive forces of nature?
First, we must have a thunderstorm, there are 4 ingredients required for the formation of severe thunderstorms that could spawn tornadoes. In meteorology we look for, S-L-I-M…or slim, which stands for Shear, lift, instability and moisture.
Moisture, lift and instability are needed for the development of thunderstorms, but the shear is what can make an ordinary thunderstorm into a severe storm capable of producing a tornado, this is what we will dig into.
Shear can come in two different forms, the first we will look at is speed shear. This is where wind speeds in a storm are slower in one area and faster in another. The second type of shear is directional, where the upper level and near surface winds are going in two different directions.
Both of these could lead to an area of rotating air parallel to the ground. It is at this point that the updraft, or lift part of the thunderstorm, comes into play as it can start to tilt this column of air. Creating a funnel and then a tornado once it contacts the ground.
This is our current understanding on how tornadoes develop, however Jana Houser, Ph.D., from Ohio University, along with her colleagues have conducted studies that show that tornadoes actually form from the ground up.
“I looked in depth at one particular case and found out for that case that there was no evidence for this top-down process occurring”, says Houser.
Houser used data from a radar that was placed on the back of a truck to complete this study. This allowed for low-level scans of the winds in a thunderstorm.
From her data, she concluded that a tornado-like vortex can be detected close to the ground, sometimes as much as a few minutes before rotation is detected in the storm by standard doppler radar towers.
She observed similar results in multiple case studies, supporting the hypothesis that tornadoes form from the ground-up.
The challenge going forward is that current radar cannot scan low to the ground, which means the future of tornado warnings is unclear.
Houser adds, “Often your eyes will deceive you when it comes to tornadoes and the formation of tornadoes. We see visually a funnel cloud descending from the cloud to the ground. Reality is that eyes are not equip to be able to see what is happening on the ground”
It remains best to seek shelter immediately if a tornado warning is issued, as a tornado could already be on the ground by the time radar detects rotation and a warning issued.