Spring is just around the corner, and it’s during these spring and summer months that we see the greatest threat for tornadoes in the Big Country. How do they form, and what are some signs to look out for when severe weather hits?
There are three ingredients that come together to create your garden-variety thunderstorm. First, we need warm and moist air at the surface to flow in from the Gulf of Mexico.
Second, we need energy! As you move from the surface to the top of the atmosphere, the air temperature has to get colder and colder the higher you go. That way, the warm and moist air at the surface, which is less dense (it weighs less), will want to rise through the cooler and more dense (heavier) air. It may be helpful to think of this like a hot air balloon rising on a cold winter morning.
The third and final ingredient for a thunderstorm is some sort of trigger to get the air moving! A low pressure system usually does the trick. A low pressure system can form on the east side of the Rocky Mountains, and with it comes some drier air that moves in from the desert southwest. As this “Dry-Line” moves east into Texas, that can cause the air at the surface to rise and get moving. Before you know it, you have thunderstorms!
For a tornado to form with one of these storms, we need one more ingredient… Shear! Shear basically means that as the altitude increases, the wind changes its speed AND direction. Shear is what causes thunderstorms to rotate as they build up into the atmosphere. Rotating thunderstorms are also called Super-Cell storm.
Tornadoes are very fast rotating columns of air that occur at the base of super-cell storms. One feature that can show up before a tornado forms is a Wall Cloud. This is a rotating “wall” of clouds that lowers below the rest of the storm. From this rotating base, a funnel cloud can tighten up and begin to drop even lower. Once there is dust/ dirt or debris at the surface beneath a funnel cloud, it can then be considered a tornado.
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-Meteorologist Avery Tomasco