An extreme storm named Boris slammed central Europe over the weekend with record rainfall, deadly flooding and up to 10 feet of mountain snow. At least 12 people have died — six in Romania, two in Poland, three in Austria and one in the Czech Republic — since the rains began Friday, according to officials.
By Dan Stillman
and The storm — which unleashed several months’ worth of rain in just a few days — was spawned by a rare combination of meteorological factors, starting with an unusually powerful outbreak of cold air in western Europe that clashed with exceptionally warm weather to the east. Human-caused climate change probably intensified the ensuing deluge by warming the air and the water that fed into the storm.
How did the storm come together?
The beginnings of Boris came as a large dip in the jet stream plunged Arctic air southward into Europe. Several stations in Austria saw record cold for the time of year as temperatures remained below 50 degrees Fahrenheit (10 degrees Celsius) for three days, while Hochfilzen in western Austria recorded its lowest September high temperature of 33 degrees Fahrenheit (0.8 degrees Celsius). Switzerland, Italy and Germany also saw historic cold.
The cold-air outbreak has a connection to usual warmth and unusually high pressure in the polar stratosphere, according to Judah Cohen, a long-range forecaster at Verisk Atmospheric and Environmental Research.
Flooding disaster unfolding right now in Central Europe.
— Scott Duncan (@ScottDuncanWX) September 15, 2024
Why is it so bad?
This thread takes a quick look at some of the key ingredients of this record-breaking storm. pic.twitter.com/xqkNpRPk9a
As the Arctic air swept southward through western and central Europe, it clashed with unusually warm, moist air to the east and south. Numerous heat records were set in Russia with temperatures soaring into the low 80s (upper 20s Celsius), according to weather historian Maximiliano Herrera. Moscow set a record for its hottest September night when the temperature only dropped to 67 degrees (19.2 degrees Celsius).
Low pressure forming near the intersection of the clashing cold and warm air masses then became cut off from the jet stream and trapped by areas of high pressure to its west and east. That caused the storm to stall over central Europe, allowing it to draw moisture-filled air from a historically warm Mediterranean Sea, which in August recorded its warmest average sea surface temperature for any month on record.
The moisture surging north and west from the Mediterranean was — in many cases — forced up mountain slopes. The rising air helped to squeeze out even more rainfall as it cooled and condensed out moisture, intensifying the downpours on the steep terrain and adjacent valleys.
Humidity that reached record levels across the planet this summer may have contributed to the heavy rainfall as well. Scientists say that warm air brought about by climate change is prone to holding more moisture and producing more intense rainfall. The nonprofit Climate Central says the atmosphere holds 4 percent more moisture for every one degree Fahrenheit of climate warming, which “supercharges” the water cycle.
How much rain and snow fell?
The result was repeated rounds of heavy rain over the same locations, triggering catastrophic flooding in the Czech Republic, Austria and Romania. The storm also dumped historic amounts of snow in the Alps. Some rain and snow totals included:
- Jesenik, Czech Republic, received 18.2 inches (463 millimeters) in four days, as much as would typically fall in about six months. 18.3 inches (464 millimeters) fell in nearby Serak.
- St. Polten, Austria, received 14.2 inches (361 millimeters) in four days, exceeding the total rainfall for the previous wettest autumn (September through November) on record, and making September the city’s wettest month in 130 years.
- In Austria, Lilenfeld and Tulin recorded four-day record rainfalls of 14.6 and 14.1 inches (371 and 358 millimeters), respectively.
- Parts of Poland saw two-thirds of its average annual rainfall in three days.
- Bratislava, Koliba, Slovakia, recorded 9.9 inches (251 millimeters), making September the wettest month since at least 1961.
- Up to 10 feet of snow fell in the Austrian Alps, where some locations reported their first September snow on record. Heavy snow also fell in the Swiss Alps.
How has the storm impacted central Europe?
Six deaths in Romania were in Galati County, Dan Cristian Ionascu, a spokesperson for the Galati Emergency Situations Inspectorate, told The Washington Post in a text message Monday. One person was missing, Ionascu added.
After visiting Pechea in Galati County, Romanian Prime Minister Marcel Ciolacu said that more than 5,000 homes were affected by the floods. “Nothing can ease the suffering of the people of Pechea,” Ciolacu wrote on Facebook.
Austrian Chancellor Karl Nehammer, who said Saturday that almost everywhere in the country had been affected by heavy rainfall or snowfall, said Sunday afternoon that the “situation remains serious.”
Thousands of firefighters and emergency workers have been deployed to tackle the floods, he said, and schools were closed Monday. Campaigning for the Sept. 29 legislative election was also paused Sunday.
“All our energy and attention is focused on disaster management and helping those affected by the storms,” Nehammer wrote on X.
Austrian public broadcaster ORF reported Monday that two men, ages 70 and 80, had died in the floodwaters in their homes in the Lower Austria villages of Untergrafendorf and Höbersdorf, respectively. A firefighter also died over the weekend after “slipping on stairs” while pumping out a flooded basement in the Austrian town of Tulln.
Infrastructure Minister Dariusz Klimczak confirmed on Polish broadcaster TVN24 that two people had died in the floods: one in the rural municipality of Kłodzko, in southwestern Poland, and a second in the south.
Prime Minister Donald Tusk wrote on X on Sunday that he had issued a disaster declaration, a step toward requesting European Union aid.
On Monday afternoon, the Polish government also announced a state of natural disaster for 30 days across several flood-affected areas.
In the Czech Republic, Prime Minister Petr Fiala spoke of a “once-in-a-century flood.” One person drowned in the Krasovka River in the Czech district of Bruntal, police confirmed Monday. At least seven people were missing.
What’s happening with the storm now?
By Monday, the severe rainfall showed little signs of easing. In the state of Upper Austria, emergency services said that new, intense rainfall was causing water levels to rise again. “We are currently monitoring the situation and waiting for a possible second wave,” Markus Voglhuber, spokesman for the state fire brigade command, told Austria’s ORF. Authorities in the state of Lower Austria warned of a high risk of dams breaking.
Flood advisories remained in place across the whole of the Czech Republic and parts of Slovakia as of Monday morning, according to Meteoalarm, a weather tool created by the European Network of National Meteorological Services.
Jason Samenow contributed to this report.
