Heavy rains fell in Greece, Bulgaria and parts of Türkiye for days. It’s usually sunny and dry there at this time of year. Why is it raining now? The so-called omega weather conditions are said to be responsible for this. Felix Plumer of SRF Meteo answers the most important questions.
What exactly is Omega Weather?
When we talk about the omega site, we are actually talking about a climate phenomenon in the upper atmosphere. Ideally, the jet stream, a strong wind band, runs from west to east at an altitude of 7,000 to 10,000 meters and separates the cold air in the north from the warm air in the south. In fact, the jet stream performs wave motions. In extreme cases, it drifts far to the north and there forms a sort of bubble, the omega high, while far to the south one low almost catches up with the other.
Why are omega layers so stable?
As it stands, the depression off the Portuguese coast and the depression over the Western Balkans and Greece have almost caught up with it. Heavy rain falls on the eastern side of this depression, not only in Greece, but also in Bulgaria and Turkey. So the two low pressure areas block each other and drain each other’s energy. Because of this blocked situation, the two depressions no longer move and rain falls in the same place for several days, which of course leads to floods. Incidentally, Spain was also hit very hard at the beginning of the week.
legend:
The damage and destruction following catastrophic floods caused by storms and heavy rains in the Pelion region (Greece) is extensive. (Registered on September 6, 2023)
imago photos
Are there other causes of heavy rain in Greece?
In addition to the blocking effect, the Mediterranean Sea is very warm. This causes a lot of evaporation. Because the air above is also very warm, it can absorb a lot of moisture and heavy rains occur. But it is a phenomenon that occurs practically every fall in the Mediterranean region, and early this fall it is simply too severe. To quantify this: In the city of Zagora in Thessaly, 750 mm of rain fell in 24 hours. For comparison: 10 days ago in Piasca there were 400 mm in 3 days, and we had the feeling that this figure was very high. The European maximum 24-hour precipitation is 1121 mm, measured in Spain in 1982.
How is the weather in Greece? Will the rain stop soon?
Omega situation with summer weather here will remain in place until the beginning of next week. However, the Daniel Depression, which brought heavy rains to Greece, is now moving towards the southeast and things are now drying out in Greece.
Could there be a rise in omega anywhere in Europe?
Yes, there are always omega layers. Also in the summer of 2003, in the summer of 2018 and last summer we were below the omega level for a very long time. The result was extreme heat and drought. If we reach high omega levels in winter, it will be very cold, with temperatures reaching around -10 degrees even during the day. This was last the case in February 2012. Conversely, in the summer of 2021, Omega was high over Eastern Europe and we were at the bottom, at the western foot of Omega. Result: We also experienced heavy rains and floods at that time.
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