What are Landspout Tornadoes?
Come spring, residents in the Central and Southern Plains become acutely aware of weather conditions. Severe weather, including tornadoes, can quickly develop and pose a significant threat to anyone in their path.
A landspout tornado is a lesser-known severe weather phenomenon that can develop without much warning. Landspout tornado outbreaks are a common occurrence in the eastern plains of Colorado and can occur in the Texas and Oklahoma Panhandles, but they are much less frequent there. Landspout tornadoes are awe-inspiring but are often misunderstood. This article will look at the science behind landspout tornadoes and address common misconceptions about them.
Formation: There are two methods by which tornadoes are thought to form: the Top-Down process and the Bottom-Up process. Most tornadoes associated with thunderstorms form by the former process, where rotation in the middle levels of the storm is concentrated and descends to the lower levels of the storm. Landspout tornadoes, however, form by the Bottom-Up process. Typically, this process occurs under a developing or rapidly intensifying thunderstorm or towering cumulus cloud. Small low-level vortices (areas of concentrated rotation) exist in abundance along certain surface boundaries, particularly nearly stationary fronts exhibiting strong wind convergence. As the strengthening updraft of the storm moves over these vortices, the upward motion acts like a vacuum, stretching the low-level vortex and tightening it into a landspout tornado. This process may be compared to a rotating figure skater: when the skater’s arms are extended, he/she spins slower; when the skater’s arms are pulled in, the rotational velocity increases. Once the storm moves away from the boundary (and the source of the low-level rotation), the landspout weakens and dissipates.
Misconceptions: Supercell tornadoes (tornadoes associated with the strongest type of thunderstorm, and thus cause the majority of damage and fatalities) tend to be the focus of severe weather-related news stories. But landspout tornadoes are rarely mentioned. As a result, there are many misconceptions about them. Here are the top three myths of landspout tornadoes.
Myth 1: Landspouts are not tornadoes.
Response: A tornado is defined as a violently rotating column of air in contact with the ground, and beneath or attached to a cumuliform cloud. While the formation process is different for landspout and mesocyclone tornadoes, both are tornadoes by definition.
Myth 2: Landspouts are weak and not dangerous.
Response: While no documented landspout is as strong as the strongest mesocyclone tornadoes, and most are usually on the weaker side, landspout tornadoes can reach EF2 to EF3 intensity (winds up to 165 mph) and can last for twenty minutes or more. In fact, they can do as much damage as a moderate tornado and should be regarded as equally dangerous. One landspout tornado outbreak that resulted in an unspecified amount of damage occurred on June 15, 1988, where F2- and F3-rated landspouts struck Denver, Colorado.
Myth 3: No wall cloud means no landspout.
Response: Since landspouts do not form from a mesocyclone, and often form beneath developing storm updrafts (although they can just as easily form beneath a well-defined storm), a wall cloud (which is a feature typically associated with supercell tornadoes) is unlikely to be present when a landspout is developing or occurring. However, the lack of a wall cloud does not mean tornado formation is unlikely. The best indicator of a tornado is a sustained and well-organized dust whirl beneath the funnel.
While landspouts are relatively unusual in the Texas and Oklahoma Panhandles, it is precisely their rarity that makes them potentially more hazardous. Landspout tornadoes are just as dangerous and capable of damage as their mesocyclonic counterparts and must be regarded with equal concern.
