Rivers overflowing their banks in Austria, Romania, the Czech Republic and Poland have already claimed lives, damaged thousands of homes and forced hundreds of people to leave their homes. In Austria and Switzerland, the slow-moving low-pressure Storm Boris, has also produced snowstorms, which are unprecedented for September.

According to Velle Toll, associate professor of climate physics at the University of Tartu, when examining the causes of Europe's unusual weather patterns, it is important to take into account changes to the planet as a whole.

"The last two years have seen record temperatures globally. This means that there is also a record amount of energy in the climate system. On the one hand, the El Niño phenomenon, which is now over, is playing a role, but so is the continued use of fossil fuels," Toll explained.

Southern Europe and the Mediterranean were hit by another blisteringly hot summer this year, with temperature records broken for the third year in a row. Record levels of water evaporated from the Mediterranean Sea due to the high temperatures, creating favorable conditions for storms to occur.

In September, however, an unprecedented cold front crossed the Atlantic into western and central Europe, colliding with the huge warm air mass that had accumulated in central Europe, and creating a sharp temperature differential. Just like when a sauna door is opened suddenly, less moisture was able to enter the cooler air and so it came down to earth as precipitation.

We then had a historic cold wave (for this early in September) plunge south out of the Arctic and through Europe.

We now have an unprecedented combination of hot and cold (ideal for strong thermal boundaries/weather fronts). pic.twitter.com/QTYv2GF7yC

— Scott Duncan (@ScottDuncanWX) September 15, 2024

As a break developed between the cold air mass that reached Europe and the low pressure area that was its source, it became trapped in central Europe.

This also provided the conditions for the storm to spread across the same areas for a long period. The region's mountains, as well as the Black Sea also play a role in amplifying the rainfall, helping to transfer moist air from the Mediterranean to the storm.

According to Toll, this is an example of how Europe's weather is largely shaped by the movement of different air masses, both in terms of where they originate and what type of air they consist of.

While due to El Niño and a number of other factors, the southern hemisphere was significantly warmer than average, the movement of air masses in the northern hemisphere was also affected.

"The record amount of energy stored in the climate system is not evenly distributed around the world. Anomalies are always stronger in some regions than in others. If we have anomalies in the global temperature distribution, then it will also cause changes in the movement of air masses," said Toll.

"The anomalies in the northern hemisphere's air mass movement are all linked," Toll explained.

"If we have one kind of anomaly in Estonia and another anomaly in central Europe, to find the causes, we have to look in the same place," he said.

For example, the people of Estonia have been enjoying some unprecedentedly warm weather due to a powerful area of high pressure over Russia. This has prevented the Atlantic cyclones that normally characterize the Estonian fall from reaching the Baltic Sea.

According to the Estonian Environment Agency, last September was Estonia's warmest on record and this year is shaping up to be similar, with several previous daily records having already broken.

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