SAN ANGELO, Texas — According to the National Weather Service, dust devils are dust-filled spirals that are created by steady surface heating. They are typically smaller and less intense than a tornado. Dust devils usually range from 10-300 feet, in diameter, with an average height of 500-1000 feet.
Usually, they will last only a few minutes, but there have been instances where they reach heights of several thousand feet and last for an hour or more. Wind speeds in larger dust devils can reach upwards of 60 mph.
Even though they are usually smaller than tornadoes, dust devils can still be destructive as they lift dust and debris into the air. Small, unsecured structures can be damaged or destroyed if they are in the path of an intense dust devil.
Dust devils form in areas of strong surface heating, the NWS says. They generally form under clear skies and calm winds, when the ground can heat to the air to temperatures above that of the ground.
This creates an unstable atmosphere, since warm air is less dense than cold air and wants to rise. The rising air then forms an area of low pressure at the surface.
The rising air and new area of low pressure will usher in a horizontal flow of warm air to the developing vortex. The rising air will then begin to rotate and increase in speed.
As more air rushes in to replace the air that is rising, the circulation is reinforced. As the air rises, it cools and eventually sinks back to the center of the vortex. Under optimal conditions, a balance between the rising, warm air and the sinking, cold air will form. This is when the dust devil would start to move around and pick up more dust, which enhances the vortex and makes it more visible to the eye.
Once the warm air is completely mixed out, or the balance is broken in another way, the dust devil will begin to dissipate.
