How does a tornado form?
Active tornado days often occur along a very strong cold front, when warm, humid air is clashing into drier, colder air. This creates a battleground in the sky with a lot of lift or instability in the atmosphere.
Tornadoes also need wind shear – change in wind speed or direction with height. Wind shear and instability (humidity) help the thunderstorm grow tall, towering over cumulonimbus clouds. These ingredients cause the winds to begin swirling. The spin begins horizontally within the thunderstorm cloud, but warm air rising creates instability so that the horizontally rotating air becomes a vertical spinning column. When this vertical spin touches the ground, a tornado has formed and anything in its path is in danger.
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