What Causes Whirlwinds?
Whirlwinds are caused by the rising of an overheated layer of air close to the ground. Whirlwinds occur when the sun heats the air near the ground to a high temperature. As the hot air quickly rises, the air around it rushes in from all directions to take its place. Where the winds meet, they whirl round and round.
As the whirlwind whirls over the ground, it picks up dust and leaves in its path, whirling them around like a miniature tornado. Whirlwinds usually last just a few minutes, and are about as high as a telephone pole.
A whirlwind seams to appear from nowhere, usually in the middle of a calm, hot summer day. It may arrive at a scorching street corner and trip from side to aids across the hot pavement, lifting stray scraps of paper and fallen leaves high over the roof tops.
It may arrive in a dry field with a soft whisper and a swirl of grasses. But the whirlwind is most at home on the prairies and the hot deserts. Whirlwinds are subdivided into two main types, the great (or major) whirlwinds and the lesser (or minor) whirlwinds.
The first category includes tornadoes, waterspouts, and landspouts. The range of atmospheric vortices constitute a continuum and are difficult to categorize definitively. Some lesser whirlwinds may sometimes form in a similar manner to greater whirlwinds with related increase in intensity.
These intermediate types include the gustnado and the fire whirl. Other lesser whirlwinds include dust devils, as well as steam devils, snow devils, debris devils, leaf devils, and shear eddies such as the mountainado and eddy whirlwinds.