WATCH: Dust devil tears up tent on Bourne softball field

By Terry Eliasen, Meteorologist, WBZ-TV Exec. Weather Producer

BOURNE - A dust devil sent players on a Bourne softball field running for cover on Sunday.

Dust devils are a fairly common phenomenon here in the summer time. Because they look and act so much like a tornado, it can be quite startling and scary. They form very quickly and in some instances can cause some minor damage. I am sure you have all seen one form on a hot, summer day. . . perhaps at a ballfield or similar open-type space.

They are typically small, often just 10-100 feet wide and also not all that tall either - maybe 500 feet or so. They are also short-lived most of the time, spinning up and dissipating in less than a minute. While wind speeds in dust devils rarely reach more than 50-60 mph, they can be quite alarming given there is no warning. And many times small and light objects can be tossed around a bit.

How do they form?

Most times they form on clear, hot, sunny days with little or no wind. The daytime heating of the ground from the sun creates an imbalance. The air near the surface heats up quickly, getting much warmer than the air directly above it. Since heated air is less dense than cooler air, the air at the ground begins to rise quickly upward. The air getting sucked up vertically causes nearby air to rush in and fill the void. As the air rises, it may tend to start rotating. . . the more it gets stretched vertically, the faster the rotation. Think of a dust devil as a hot-air chimney of sorts: sucking up the hotter air near the ground, shooting it upwards and out of the top of the spinning vortex.

It is a rather delicate balance though and most times within a minute or less, the cycle is broken. The supply of warm air may be cutoff or a small change in terrain occurs and as quickly as it forms, it is gone.

Dust devils are much more numerous in the desert Southwest where there is typically plenty of hot air and flat terrain.