Zach’s Weather Whys: Severe storms

Zach's Weather Whys

PEORIA, Ill. — Severe storms are no doubt a deadly freak of nature, but did you ever wonder how they form?

A thunderstorm becomes severe when it contains at least one of the following. It either has hail stones of one inch or greater, winds gusts over 57 miles per hour, or a tornado. There’s four key ingredients needed to create a severe storm.

Meteorologists made an easy acronym for this called SIIM.

The “S” stands for shear, which is the changing of the wind direction as you go up in height. This wind change gives the air some spin and you typically need a certain amount of shear for tornadoes to form.

The second component is lift. A cold or warm front will give the atmosphere a much-needed boost to build the big, bad looking clouds known as cumulonimbus clouds. The taller the clouds, the more volatile the storms tend to be.

The next factor is instability. You’ve probably heard the term thrown around but what does it mean? Well, the sun heats the air at the surface and once a pocket of air becomes warmer and less dense than the surrounding atmosphere, it rises on its own, just like a balloon. The balloon or parcel of air is then considered unstable because it can rise on its own without the help of any other weather feature pushing it upwards.

Last but not least, you have to have enough moisture. You cannot build clouds without plenty of water vapor in the air. A dry atmosphere will bring minimal cloud cover which will prevent any kind of rain or storms. 

Once you combine all four of the main ingredients together, you are sure to get a severe storm.

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