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Weather tracker: Omega block brings torrential rain to Greece and Spain

This week, there was an Omega block over Europe, which caused people to experience harsh weather. A synoptic configuration known as a "Omega block" has a high-pressure area sandwiched between two low-pressure areas, giving it the shape of the Greek letter omega.

This configuration let storm Daniel form over the Ionian Sea, which led to catastrophic floods in central and eastern Greece. The moisture required for this storm was also produced by the region's warm oceans at this time of year.

On Monday, September 4, Daniel moved inland over the Balkans, causing the area to experience heavy downpours and thunderstorms. The most affected area was Central Greece, which experienced some of the worst daily rainfall totals there since 2006. In less than 24 hours, more than half a meter of rain was measured by at least two rain gauges. According to, 754mm was recorded in less than 24 hours at a station in the Pelion peninsula village of Zagora, breaking the previous record of 644.7mm set in Paliki, Cephalonia, in September 2020. When compared to the city of Volos, which lies around 10 miles to the southwest of Zagora, where the average annual rainfall is 802mm, over a year's worth of rain poured in a single day.

At this time, this storm has been responsible for 11 fatalities in Greece, Turkey, and Bulgaria. Several landslides have also been reported on the nearby Greek island of Skiathos.

Due to a cutoff low pressure system in the western Mediterranean, Spain has also experienced some severe rain this week. Cutoff lows can be associated with large daily rainfall totals because they are isolated from the main flow and so move more slowly. Therefore, a rain red signal was issued for the Madrid region on Sunday. On Monday, thunderstorms spread over Spain, causing rivers to overflow their banks to the south-west of Madrid, flooding the city's streets, and closing the metro system. In addition, on September 2 in Mas de Barberans, Catalonia, 240mm of rain fell in just 24 hours, the most in the area in the previous 23 years.

Temperatures have been between 5C and 10C above seasonal normal in central and northern Europe over the previous several days, including the UK. This trend is anticipated to last through the weekend and into the next week.