Meteorologist explains

How the tornado formed over the city center of Graz

There are three to five tornadoes per year in Austria.

(Bild: Dennis Messner)

On Tuesday, the most violent storms of the year so far took place in Styria. While the district of Weiz had to contend with severe flooding, Graz was hit by a small tornado. How could it develop in the middle of the city? And are air vortices of this kind becoming more frequent? A meteorologist provides information.

Many people in Graz could hardly believe their eyes on Tuesday: a small tornado was brewing over the city in the evening. It originated over the Plabutsch and moved across the districts of the west of Graz - it was clearly visible in Eggenberg, for example.

However, this dangerous natural spectacle is not as unusual in this country as you might think, says Christoph Matella, meteorologist at Ubimet. He even calls the Graz area a "tornado hotspot" compared to the rest of Austria. "Austria-wide, there are three to five tornadoes per year," explains the expert. What was rather unusual was that it formed over the city area of all places, which attracted many onlookers.

Tornado over Wiener Neustadt claimed 34 lives
However, the number of Austrian tornadoes is put into perspective by international comparison. In the USA, for example, around 1,200 storms of this type are registered every year - some of them with severe consequences. The most devastating Austrian tornado to date hit Wiener Neustadt in 1916, killing at least 34 people. In 2021, a dangerous air vortex on the Lower Austrian border also claimed several lives.

Tornadoes often occur when different air currents collide - this is called wind convergence.

(Bild: Krone KREATIV, Quelle: dpa)

However, these strong tornadoes differ significantly from the one in Graz in terms of their wind speed. "Strong tornadoes like the ones in the USA have speeds of over 200 km/h. Not much can withstand them and debris is whirled around," explains Matella. The one over the Styrian capital probably only reached 100 km/h and only caused minor damage such as fallen trees and loose roof tiles. Silence returned after a few minutes.

Strong tornadoes like those in the USA have a speed of over 200 km/h. Not much can withstand it and debris is whirled around.

Christoph Matella, Meteorologe bei Ubimet

Two types of tornadoes can also be distinguished in their formation. More violent storms are caused by so-called supercells. They are therefore the result of extremely charged storms. "Type two tornadoes are caused by wind convergences," explains Matella. Winds from different directions converged on Tuesday evening and the clouds were particularly low - so the conditions were ideal.

Could air vortices like the one over Graz become more frequent? It's impossible to say for sure, even in the context of climate change, says the meteorologist. "Tornadoes occur very locally and irregularly," explains Matella. "But observations are increasing because everyone has a smartphone." At best, the next storm is not expected any time soon: Although the week will remain unsettled in Styria, storms like the one on Tuesday are not expected.