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Most of the time, it is pretty easy to figure out what types of weather phenomena we need to avoid while skydiving. Thunderstorms? Check. Strong and gusty winds? Check. Extremely cold temperatures? Check. Solid clouds at or below 2,000 feet? Sure. But there is a sneaky little devil out there that has killed and injured several skydivers, and some of them never saw it coming: the dust devil. Dust devils are nothing to fool around with, especially while under canopy. And even though we often see and hear about them popping up in the desert, dust devils can actually form just about anywhere.
Dust devils are essentially mini-tornadoes. With wind speeds as high as 75 mph, they can rise from the surface up to several thousand feet (although most of them top out between 500 and 1,000 feet). Dust devils form when the sun heats the ground, usually in places where there are two different types of surface areas such as asphalt next to grass, a common situation at most drop zones. When hot air begins to rise from the surface into the cooler air above, it creates an unstable air mass. Since the hot air is less dense and lighter than the cooler air above it, the hot air rises and can begin to rotate and compress horizontally as the rotation increases, forming a tight, spiraling column of air. Voilà, a dust devil is born. You should also keep in mind that a dust devil will form when weather conditions are relatively calm, there is little or no wind and the DZ is under clear skies: in other words, during perfect jumping conditions!
Skydivers who jump at drop zones in desert locations are accustomed to seeing dust devils recklessly wandering across the airport during the warmer months. The dust and debris in a desert environment make them easy to spot, and that’s a good thing, because if you can see the dust devil, you can usually avoid it. But many dust devils are nearly impossible to see, and that is where the real hazard exists as far as skydivers are concerned. If the dust devil forms over grass, asphalt or other surfaces with very little debris that it can pull into the air, the whirling column of air can be nearly invisible.
In the past decade, at least one skydiver has died and several have suffered injuries after flying their canopies through dust devils. The fatal injury occurred to a jumper who had already landed when a dust devil re-inflated his canopy and picked him up approximately 50 feet. His canopy then collapsed, and he fell to the ground with it mostly deflated. The impact killed him instantly. Many of the injured jumpers suffered hard landings under canopies that reacted violently when they flew through nearly invisible dust devils at low altitudes.
Does this mean you should sell your gear and take up bowling for fear of a nearly invisible hazard? Probably not, but you do need to be aware of the hazards of dust devils and the fact that they can develop almost anywhere in the right weather conditions. Keep an eye out for telltale signs of turbulent air when the temperatures increase. Hopefully, you will just encounter a bit of bumpy air and turbulence when the warm air starts rising. If you are under canopy and do see signs of a dust devil, steer to avoid it if you can safely make the turn without causing a collision with another canopy or striking the ground while still in the turn. The best way to avoid injuries caused by dust devils is to recognize the environmental conditions that cause them and, during those times, vigilantly scan for and avoid them if at all possible.
—Jim Crouch | D-16979
USPA Director of Safety & Training