Of particular interest is the phenomenon of Foen type downwinds, which will return to our country.
The director of EMY, Thodoris Kolidas, on the occasion of the weather of the next few days, was the one who talked about Foen-type winds in his previous post.
Specifically in his post he states:
“Many times we have seen similar or even greater differences of 16°C between North-West Greece and Southern Island areas, especially in cases where strong southerly winds prevail. Of course we are not referring to something “unprecedented”, such as e.g. for today’s 28 °C in Heraklion and 11 to 12 °C in the northwest.
Tomorrow Tuesday we may catch even higher prices (the 30s), but they won’t be many, as reported in the press. These values will be limited mainly in Crete, or where the locally strengthened Foen-type descending winds will again play an important role”
What are Foen winds?
Downwinds, according to meteo.gr, are the strong winds that blow on the leeward side of a mountain mass and descend towards its foothills. The maximum intensity of the winds is located in the foothills and weakens significantly at a short distance from the mountain mass. Downwinds can be either warm, in which case they are usually called foehn, or cold, in which case they are called bora. In our country, downward winds of the foehn type usually occur, while its most common name is libas.
Warm Foehn Downslope Winds
The term was originally used for the dry and warm winds that are created on the leeward side of the Alps, but then prevailed as a term for local winds created by this mechanism in many regions of the Earth.
How are Foehn winds created?
A basic condition is that there is a high vertical obstacle to the wind flow, such as a mountain range. The air is initially forced to rise on the windward side of the mountain mass, where by condensing its water vapor it forms clouds and in some cases gives rain, storms or snowfall, while it then descends on the leeward side of the mountain mass where it dries and warms at a rate of about 10ºC per 1 km.
The result of the flow of this wind, as shown in the figure below, is the rise of the temperature on the leeward side of the mountain mass to levels higher than the initial temperature of the air mass on its leeward side.
In the Greek area, foehn downwinds usually occur in North Crete when strong southerly winds blow, in South Crete when strong northerly winds blow, while quite often they also appear in the eastern continental parts when strong westerly winds prevail or in Western Greece when easterly winds prevail to northeast directions.
Typical is the example of the strong downward winds in North Crete on Saturday 17/04/2021, where during the breath of the winds with different directions, the temperature rose and fell by up to 13 degrees in a few minutes.
The measurements come from the weather station in the area of Kampoi Keramion, Chania, which belongs to the network of automatic weather stations of the National Observatory of Athens / meteo.gr.
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