Over the weekend, a 5NEWS viewer, Marlene Graves, contacted us about damage from a dust devil in Delaware, Arkansas which is just west of Russellville.
So what is a dust devil? (The picture of dust devils here are from Arizona)
Dust devils look like tornadoes and are more common (or at least visible) in the SW part of the United States where there is more loose soil such as sand to show the funnel. It’s also (usually) much hotter in the southwest so the differential heating is more significant.
At peak heating during the day, warm air over a parking lot will heat faster than warm air over a field. The result is a temperature gradient. As the warmer air starts to rise it draws in air from all around it. If there is slightly cooler air above it, it may rise faster and start to spin. Due to a law in physics called “the conservation of angular momentum” the funnel wind speeds accelerate as the tube is stretched. The usual analogies are “like an ice skater pulling in their arms to spin faster” or “like a tetherball swinging around a pole”. The average wind speed from a dust devil is around 45mph but sometimes they can reach speeds of 70mph and are usually rare.
This picture shows damage to the sheet metal of a poultry operation. Winds were likely at least 40mph and probably stronger. The end of a dust devil will occur when colder air is drawn into the circulation effectively ending the updraft of warm air and ending the dust devil.
Here are the damage pictures from Delaware, AR.
(*EDIT: Received the following email from Marlene today and here’s her account of how the dust devil occurred and the time of day. “Sunday July 1,2012 at 3:38 is when the dust devil was seen. Debris was taken high into the air basically sucked up over ridge and trees towards the river. 4 chicken houses were damaged. Cattle and horses ran. The dirt devil was seen by a family member driving up the road on our land. She stated the debris got do high it looked small (large pieces of tin and insulation ). There was nothing different about the day or sky. Some light wind. We had been at the houses about 30 minutes before it hit.”)
