Landspouts are a weather phenomenon often misunderstood by the public. While not as powerful as supercell tornadoes, these rotating columns of air can cause fatalities, injuries, and significant property destruction. Despite their weaker intensity, landspouts are a serious weather event.
Defining a Landspout
A landspout is a type of tornado that develops from a cumulus cloud, rather than from a rotating supercell thunderstorm. They often appear as narrow, rope-like columns of rotating air that extend from the base of a growing cumulus congestus or cumulonimbus cloud to the ground. Unlike dust devils, which form under clear skies, landspouts are directly connected to a developing storm’s updraft. They are considered true tornadoes because they involve a rapidly rotating column of air in contact with both the surface and a cloud.
Landspouts are often described as resembling a waterspout over land due to their similar appearance and formation. They typically occur during the growth stage of a parent cloud without a pre-existing mid-level mesocyclone, unlike supercell thunderstorms. Many landspouts are initially observed as swirling debris at the surface before a visible condensation funnel fills in. This characteristic visual development helps differentiate them from other atmospheric circulations.
Potential for Harm
While generally weaker than supercell tornadoes, landspouts can still inflict substantial harm. They typically register on the lower end of the Enhanced Fujita (EF) scale, often classified as EF0 or EF1. Even at these intensities, wind speeds can reach up to 100 mph, capable of causing notable damage. Some landspouts have even been strong enough to produce EF2 and EF3 damage, highlighting their potential for significant impact.
These tornadoes can break tree branches, uproot shallow-rooted trees, and cause minor structural damage. They can also damage roofs and outbuildings, overturn mobile homes, and push vehicles off roads. Their unexpected nature increases danger, as they are often difficult for Doppler weather radar to detect due to their smaller size. This can lead to little warning time, increasing the risk of injuries or fatalities.
How Landspouts Develop
Landspout formation involves a unique meteorological process that differs significantly from supercell tornadoes. Landspouts form “bottom-up,” meaning their rotation originates near the ground. This process begins with pre-existing circulation in the boundary layer, the lowest part of the atmosphere. This low-level rotation often forms along boundaries where winds converge, such as outflow boundaries from thunderstorms or terrain features.
As a developing cumulus cloud moves overhead, its strong updraft stretches this pre-existing ground-level circulation vertically. This stretching causes the column of air to narrow and spin faster, similar to a figure skater pulling in their arms. The rotating column then extends upward, connecting with the cloud’s base and forming the visible landspout. This “bottom-up” mechanism stands in contrast to supercell tornadoes, which form “top-down” from a rotating mesocyclone within the thunderstorm itself.
Safety Measures
Despite their lower intensity, landspouts should be treated with caution. Specific safety measures can help protect individuals and property. If a landspout is sighted or a warning issued, seek sturdy shelter immediately. The safest place is an interior room on the lowest floor of a robust building, away from windows.
Mobile homes and vehicles offer little protection from the winds and flying debris associated with landspouts and should be avoided. It is important to stay informed about local weather alerts through official sources. While landspouts can be difficult to detect by radar, local observations and reports can provide valuable warning. Remaining aware of your surroundings and having an immediate action plan can reduce risk during these events.