Storm that wreaked havoc in Montana not a tornado but a landspout

A storm that swept through Montana, Pretoria North, on February 18, damaging multiple vehicles and buildings, was a landspout, not a tornado, the South African Weather Service (Saws) has confirmed.

Analysis of the event included site visits and a study of high-resolution satellite images.

Saws had an orange level 5 impact-based weather warning in place over Gauteng and adjacent provinces for disruptive rainfall and/or localised flooding at the time of the incident. 

According to the weather service, a landspout develops over land and is generally smaller and weaker than a  tornado, which is a violent rotating column of air that extends from a thunderstorm and measures less than a few hundred metres in diameter, though some are larger than 1km.

“Tornadoes and landspouts are two small-sized events the Saws is working to nowcast for the benefit of the public. Unlike other weather conditions, signs of the potential development of a tornado are evasive, particularly for landspouts. However, there has been an instance where the Saws issued a tornado warning before its formation [December 30 2017), albeit four minutes before it struck.

“Tornadoes and landspouts have a similar appearance but their development mechanisms and strengths differ. It is for this reason that the Saws conducted a thorough analysis in Montana after which it concluded the event was a landspout. This landspout developed shortly before 5pm local time and affected a short stretch to the busy Sefako Makgato Drive (R513). From there it uprooted trees and remained on one side of the main road.”

Eyewitnesses estimated the landspout lasted less than five minutes before lifting and disappearing. 

“The trace of its weakened phase was noted towards Zambezi where only tree branches were broken off with a zigzagging motion to the right side and back to the left of the main road. Here, carport awnings and more roof sheeting were broken, twisted and lofted into the air. It is miraculous that, to date, no reports of deaths or injuries have been received.”

The weather service said the landspout was rated as an EF0 according to the Enhanced Fujita scale for tornado intensity, which is used internationally. 

“An EF0 event is generally associated with light or minor damage and corresponds to estimated wind speeds of 90km/h to 130km/h.”

Saws advice on what to do when a landspout or tornado strikes:

• Where possible, quickly get out of the zone where two thunderclouds are moving. Within such zones it is almost certain the wind will be strong and potentially damaging with injurious debris. Community members at the sudden start of a tornado or landspout may be caught by surprise, but each next minute should be used effectively.
• Do not use a tree as shelter when it is in the path of a tornado or landspout.
• Loud sounds associated with tornadic impacts should quickly be used to scan the direction of clouds some distance away from the tornado/landspout. Thereafter, move out of the path of this event before moving opposite the main direction of clouds. Then find refuge.    
• When indoors in a formal house, remain in a small room, such as the bathroom.  
• To minimise the impact for shack dwellers, use the inside of small furniture such as a side wardrobe.

 TimesLIVE