How do tornadoes form?

Weather News

(WWLP) – We’ve had three tornadoes in Massachusetts in just the last few weeks, including one over this past weekend.

What conditions are necessary to create a tornado? 22News Storm Team Meteorologist explains.

Related: National Weather Service confirms tornado in Webster during Saturday storm

In order to create a tornado you need a rotating thunderstorm with ingredients that you can remember using the acronym SLIM: shear, lift, instability, and moisture.

Shear is the change in wind speed or direction. Lift helps air to start rising, and instability keeps the air rising. Moisture is high dew points and high humidity levels.

So once you’ve got the ingredients for a strong thunderstorm, then you need the ingredients for a tornado. For that, you need to look at the lowest 1000 feet of the atmosphere, just above the surface. 

In that lower atmosphere, you need a short distance from the base of the cloud to the ground and that means you need the a low cloud base. Secondly, you need to make sure your high humidity, directional wind shear (rotation) and instability are in abundance in the lower atmosphere.

Sometimes you can have all these ingredients and a tornado does not form, therein lies the challenge in forecasting tornadoes.

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