We've all heard of tornadoes, but what in the world is a "landspout"? A landspout is actually a type of tornado that forms from the ground, up. The official meteorological term for a landspout is "non-supercell" tornado. They form on days with low vertical shear and high temperatures. They usually require some sort of localized boundary of differing types of air masses. This might be an old outflow boundary from a previous thunderstorm, or preferably a convergence boundary formed by differential wind patterns. As winds converge along the boundary, zones of horizontal speed-shear develop. What happens is, air closer to the surface flows in one direction while the air above it flows in another. You can see how this may cause the air to "roll" horizontally in the form of an invisible tube. As these "vortex tubes" begin to rotate around a horizontal axis, they spin faster and faster. Now, add the vertical ingredient of the updraft region of a growing cumulus cloud over top of the vortex tube. The tube now becomes becomes vertically oriented, retaining its spin. The strong updraft draws the vortex tube up to the cloud base. Now we have a rapidly-spinning tube of air that started at ground-level, and is drawn up to the cloud base...a landspout! Landspouts have been known to cause considerable damage if they move into populated areas. They can often surprise people, even weather forecasters, because they usually form in non-severe weather situations, such as underneath a growing cumulus cloud.
You can often see landspouts on the eastern plains of Colorado just east of Denver International Airport on hot summer days as the cumulus clouds are beginning to grow before the afternoon thunderstorms start. Pictured to the left is a landspout that formed near Aurora, CO a few years ago. It moved through a housing development that was under construction, and threw some lumber around. By the way, this type tornado, when formed over water, is called a "waterspout".
Landspouts are officially considered a form of tornado by the National Weather Service and most meteorologists. The more widely-known "supercell" tornadoes form under the rotating base of a supercell thunderstorm, extending from the cloud downward to the surface. A landspout forms near the surface, then grows upward to the cloud base. Landspouts are the more common type of tornado and are generally less destructive than supercell tornadoes. However, landspouts are capable of EF-1 damage or higher, so we don't advise driving right up to one.
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