What is a supercell and how is it different compared to a thunderstorm

In our series dedicated to extreme weather events, we wrote about thunderstorms and explained how these phenomena affect us. Briefly, a thunderstorm is an extreme weather event that occurs when moisture and unstable air rises quickly from the ground. As the sun heats up the air above the ground during summer, sometimes this warm air is forced upwards quickly. Since hot air is less dense than cold air, it will continue to rise until it reaches the higher parts of the atmosphere in a process known as convection.

Usually, a thunderstorm doesn't last more than an hour and covers a fairly small area, usually not enough to even cover an entire larger city, such as Bucharest.

Supercells, however, are different, in the way that they get much bigger, can last for several hours and cover potentially hundreds of kilometers, so entire regions of a country, instead of barely a city. The principle is the same as with a regular storm. Warmer, moist air sits closer to the ground, while cooler air blows upwards in a different direction, which generates atmospheric instability.

The Weather Channel explains that the reason why supercells last so much longer is the wind shear. This phenomenon occurs when winds above ground form and blow in a different direction compared to winds close to the ground, causing the air in between to start spinning on a horizontal axis.

In the case of high wind shear, the upward current of a thunderstorm changes the way the air spins from plain horizontal to an upward direction. At the same time, the storm also stretches vertically, with this tube-like part becoming the supercell's "mesocyclone".

This rotating column found inside of the storm is what causes the supercell to last as much as hours at a time and has the potential to transform it into a tornado with very powerful winds.

A supercell can reach heights of up to over 12.000-18.000 meters high, giving the impression of a never-ending vertical storm.

How frequent supercells could become in Europe

While supercells have been so far specific to North America, especially the Midwest where many tornados form every year, scientists warn that these types of storms will begin to form more often in Europe, as well. According to Euronews.green, powerful thunderstorms were the single most destructive form of natural disaster in 2023, accounting for almost 55 billion euros worth of insurance loss claims.

In July 2025, Bucharest and neighboring areas were hit by a severe supercell thunderstorm that ripped trees out of the ground and even roofs from the top of buildings, leading to the death of a woman, who was hit by debris from a collapsed roof.

France and Italy have been hit by supercells this summer themselves, alongside other regions from Europe, with scientists now looking to intensify their research in understanding and predicting when and how these storms are likely to form.

The problem with tracking supercells in Europe lays not only within the fact that these phenomena take place in rare occasions, but also due to inconsistencies within the countries' national weather radar systems.

Monika Feldmann, from the Mobiliar Lab for Natural Risks and the Oeschger Centre for Climate Change Research at the University of Bern, Switzerland, says that this makes cross-border detection of these storms more difficult and inconsistent.

This is why researchers from these institutions, alongside scientists at ETH Zurich, developed a highly-detailed simulation model. The model uses very accurate maps in order to simulate super cells at a very fine level of detail.

This is how they were able to discover that the Alps are a potential hot-spot for supercells in Europe, as this region experiences some 38 such storms every season on its northern side, while the southern part of the Alps is hit by up to 61 supercells per summer.

The research from Swiss scientists reveals that a 3 degree Celsius warming of the atmosphere in this area could lead to a 50% increase in the number of supercells, with each storm becoming more powerful or long-lasting, as well.

This is for countries located in mountainous regions, such as Germany or Austria, while France or Spain could potentially see a decrease in the number of supercell storms.

Feldmann says that "these regional differences illustrate the diverse effects of climate change".

How to prepare for a supercell

Being a more powerful thunderstorm, the advice from our original article applies here, just supercharged, if you will. Supercells hit differently than a normal thunderstorm, because you never know for sure if you're close to the center of the storm or more towards its extremities.

This can mean that it will either pass quickly and without any damage for you or it can bring strong winds, lots of precipitation and even hail.

Generally speaking, make sure that you don't leave lightweight objects outside in your yard or balcony, especially during thunderstorm season, which in Romania for example happens around mid to late-July. Also, if you plan to leave your house for hours at a time during summer, don't leave any windows open.

At the same time, trimming the trees around the streets and in your own yard is crucial to prevent severe damage, while checking the weather application for constant updates helps. And it also helps to check on the weather forecast from previous years, to get an idea of when it's more likely for a supercell to form, although again, you can never predict it 100% on your own and it's difficult even for meteorologists to track it down early-on.