Landspout

Characteristics

Landspouts are a type of tornado that forms during the growth stage of a cumulus congestus or occasionally a cumulonimbus cloud when an updraft stretches boundary layer vorticity upward into a vertical axis and tightens it into a strong vortex. The parent clouds are often predominantly liquid when producing landspouts. Landspouts can also occur due to interactions from outflow boundaries, as they can occasionally cause enhanced convergence and vorticity at the surface. These generally are smaller and weaker than supercell tornadoes and do not form from a mesocyclone or pre-existing rotation in the cloud. Landspouts can form in the flanking line of supercell thunderstorms, following the predominant formation area of landspouts in general within updraft zones without undercutting downdrafts. Because of this lower depth, smaller size, and weaker intensity, landspouts are rarely detected by Doppler weather radar.

Landspouts share a strong resemblance and development process to that of waterspouts, usually taking the form of a translucent and highly laminar helical tube. "They are typically narrow, rope-like condensation funnels that form while the thunderstorm cloud is still growing and there is no rotating updraft", according to the National Weather Service (NWS). Landspouts are considered tornadoes since a rapidly rotating column of air is in contact with both the surface and a cumuliform cloud. Not all landspouts are visible, and many are first sighted as debris swirling at the surface before eventually filling in with condensation and dust.

Orography can influence landspout (and even mesocyclone tornado) formation. A notable example is the propensity for landspout occurrence in the Denver Convergence Vorticity Zone (DCVZ).

Life cycle

Forming in relation to misocyclones and under updrafts, a landspout generally lasts for less than 15 minutes; however, they can persist substantially longer, and produce significant damage. Landspouts tend to progress through recognizable stages of formation, maturation, and dissipation, and usually decay when a downdraft or significant precipitation (outflow) occur nearby. They may form in lines or groups of multiple landspouts.

Mesocyclone transition

Rarely, a landspout may transition into a mesocyclonic tornado if the attendant misocyclone merges into a stronger mesocyclone.

Damage

Landspouts are usually weak, typically not surpassing the EF0 category. However, on rare occasions, they have been observed to reach up to EF2 and EF3 intensity.

Examples of such unusually strong landspouts include:

• The June 7th, 2021 Weld County Tornado — rated EF2;
• The May 26th, 2018 – Podkońce, Poland Tornado — rated F2 (later upgraded to IF2);
• The June 15th, 1988 Tornado Outbreak, during which 4 landspouts struck the areas in and around the city of Denver, Colorado. Two of them were rated F1, one — F2, and another one — F3.

References

References

1. Judson Jones. (21 May 2020). "Why Landspout Tornadoes are Common in Colorado".
2. Bluestein, Howard B.. (1985). "A History of Severe-Storm-Intercept Field Programs". Weather and Forecasting.
3. American Meteorological Society. (2000). "Glossary of Meteorology, Second Edition".
4. (1 April 2009). "Proposed Conceptual Taxonomy for Proper Identification and Classification of Tornado Events". Weather and Forecasting.
5. Wakimoto, Roger M.. (1989). "Non-supercell Tornadoes". Monthly Weather Review.
6. Judson Jones. (8 June 2021). "The No. 1 US county for producing tornadoes just spawned another landspout".
7. Szoke, Edward J.. (8 Nov 2006). "The Denver Cyclone and Tornadoes 25 Years later: The Continued Challenge of Predicting Non-supercell Tornadoes". [[American Meteorological Society]].
8. Szoke, E.J.. (1990). "A decade of tornado occurrence associated with a mesoscale flow feature: The Denver Cyclone". [[American Meteorological Society]].
9. Forbes. (1983). "A Concentrated Outbreak of Tornadoes, Downbursts and Microbursts, and Implications Regarding Vortex Classification". Monthly Weather Review.
10. "Tornado Facts".
11. "Storm Spotter Field Guide: Non-supercell Tornadoes".
12. (Summer 2014). "Landspout Tornadoes continued...". José Garcia.
13. "June 7th, 2021 Weld County Tornado".
14. "Storm Events Database June 7, 2021". National Centers for Environmental Information.
15. "European Severe Weather Database". European Severe Storms Laboratory.
16. "Tornado Archive".
17. (October 1990). "A Satellite Perspective of the June 15, 1988 Tornado Outbreak in Denver, Colorado". American Meteorological Society.