Fohn...

[Anakin]

Whereabouts are you, Anakin? Can you add your exact location, which I guess is somewhere in Italy? Thanks

Done :blush:

[stormchaser1]

Afternoon everyone

Just found this extract about the FOHN effect in one of my weather books

Another kind or orographic wind is the trans- mountain wind such as the chinook, the fohn and the zonda. Rather than go around the mountains and through the valleys, the second option for moving air when it meets a mountain is to go up and over it. When air is lifted up by the sloping terrain, the increasing altitude causes it to cool and expand. The water vapour it carries reaches its dew point, condenses and forms clouds. This process can lead to some unusual phenomena: a single mountain such as Mount washington, in new Hampshire, USA, is so tall that it wears a cloud on its summit more or less all the time.

At other times, conditions may be right for what is kwon as th FOHN effect [named after the hot, dry winds that roar through the Alpine valleys], a variable phenomena which is responsible for small- scale weather patterns known as micro- climates. A fohn wind carries moisture- laden air high up mountainsides. As it rises the temperature falls about 0. 5c [33f] for every 100m [330 ft] in elevation. Cooling causes the water vapour to conndense, creating clouds which sometimes drop rain or snow on the windward side of the mountains. In the process, much of the water content in the air is effectively "wrung out", so, once it has reached the top, the cooled dry air starts to rush down the otherside, the leeward side, where it is warmed up by compression and begins to generate heat at the rate of roughly 1c [33.8 f] for every 100m [330ft] it falls. The drier the air, the faster the rise in temperature. Consequently opposite sides of the same mountain can have radically differant weather- at the same time ! The most dramatic examples of the FOHN effect are the Andean Zonda, and the chinook, which blows down the eastern slopes of the Rocky Mountains. The FOHn effect is not without its dangers; In winter, the rapidly warming air can cause snow to melt quickly and trigger avalanches

nigel