Genoa low over Poland

The ever-intensifying global warming amplifies frequency and magnitude of extreme weather events. After months or insufficient rainfall and consequent drought, the tide has turned. The Mediterranean Sea, whose temperature is affected by a massive heat wave, in early July 2025 ran 6 Celsius degrees higher than usually at this time of year, produced masses of water vapour. The evaporated water formed rainclouds, which drifted towards central Europe, in a language of meteorology as part of a low pressure system, called Genoa low.

The very existence of the Genoa low and its abundance in rainfall are not a problem itself. The hazardous nature is driven by its co-existence with an anticyclone, which does not let rainclouds roll by and spread precipitation over large swathes of land. Instead, a strong anticyclone renders the Genoa low stationary, which effects in several hours of solid rainfall in a specific area. Such situation happened in September 2024 and resulted in severe, though confined to a few towns, flooding in south-western Poland.

This time the forecasts were not alarming as then, but pointed at serious peril of intense rainfall in Śląsk Cieszyński. A serious risk of above-average precipitation was clear in forward-looking visualisations over a week ago. The scale of a potential disaster, however, was unknown until last moment. Genoa lows are poorly predictable, an anticyclone’s behaviour is the core unknown variable. The less stationary a low is and the less abrupt its nature, the lower the risk of flood.

This year the precedent drought has effectively reduced danger of a major flood, however local flash floods were quite conceivable, especially since dried-up soil could have difficulty absorbing large amounts of rainwater.

The rainfall began on Tuesday, 8 July and has lasted until now. It turned out to be far less intense than predicted and wreaked less havoc than many feared. Preventive actions have been taken to avert a disaster witness mere 10 months earlier in similar circumstances.

Countrywide there have been no submerged inhabited areas and no major losses were reported.

In Warsaw no records have been broken. The highest one day precipitation over the last week reached 24 millimetres (vs. 93.8 millimetres of rain fallen on 19 August 2024). Also the monthly record of the wettest July, set in 2011 (295.8 millimetres over the entire month) seems unthreatened as of now (so far the accumulated precipitation in the first 12 days of the month totalled 28 millimetres. Next days are to bring moderately wet high summer, with no extreme weather. May heat waves and other radical events pass Warsaw by!