Dust devils: little whirlwinds of the prairie
On a hot, sunny, calm day, a spinning column of dust can suddenly rise from a field or a gravel lot, dance along for a minute, and vanish. It looks like a tiny tornado, but it isn’t one.
How a dust devil forms
- Hot ground: strong sunshine heats bare ground, such as a ploughed field, a dirt road or a parking lot, and the air right above it gets very warm.
- A bubble rises: a pocket of that hot air starts to rise quickly, and air rushes in along the ground to replace it.
- It starts to spin: any little twist in that incoming air gets tightened as the column stretches upward, the way a figure skater spins faster when they pull their arms in.
- Dust makes it visible: the spinning air picks up dust, straw and leaves, so we can see it.
It fades when it runs out of hot air to feed it, often after just a few minutes.
Dust devil or tornado?
- Where it starts: a dust devil starts at the ground and builds upward, in clear, sunny weather. A tornado hangs down from a thunderstorm cloud.
- Size: most dust devils are about 3 to 90 metres across and a few hundred metres tall.
- Strength: most are weak and short-lived. Larger ones can reach about 100 km/h, much less than a strong tornado.
- Sky: if there’s no storm cloud overhead, it’s almost certainly a dust devil. If there is, treat it as a possible tornado (or a landspout) and take shelter.
Where to spot one
Look on sunny, light-wind days, especially where hot bare ground meets cooler ground: the edge of a dry field next to an irrigated one, a gravel road, a construction site or a parking lot. Around Lethbridge, the big open fields in spring before the crops cover the ground are a good bet. Late morning to early afternoon, when the ground is hottest, is the best time.
Learn more
- Dust devils, U.S. National Weather Service, Flagstaff
- Tornadoes on the Prairies
Source: U.S. National Weather Service, Flagstaff office (formation, size, wind speed and timing).
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