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Old 11.08.2009, 08:55
Solates Solates is offline
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Re: Föhn Yesterday?

Thanks for the replies but I think this informative reply from puts this one to bed! Some concise information here for anyone interested in diagnosing Föhn events.

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"I was working on late shift on Sunday 9th August, and I haven't seen Foehn in any part of Switzerland. In the Zurich area, there was slight Bise (NE) flow in the lower part of the atmosphere, while only in the upper levels there were light southwesterlies.

Detection of Foehn winds on ground is not always and not everywhere an easy task. Check out both the temperatures, relative humidities and winds (speed and direction) on our website if you want to diagnose Foehn occurence:

Characteristics of the typical Foehn air are its warmth and dryness. Temperatures in the alpine valleys frequently exceed surrounding values in flat areas by several degrees Celsius, especiallly in winter and autumn Foehn situations. At the same time the relative humidity is very low, some 20 to 40%, while in non-Foehn areas it's rather 40-60%. Since in the Zurich area Foehn is a rare event and mostly occuring on warm or even hot spring or summer days, the Foehn air does not differ that much from the surrounding non-Foehn air, as in the alpine valleys.

Wind direction is another check, then, to diagnose possibility of Foehn: at weather stations Zurich-Fluntern, Zurich-Kloten and Waedenswil, Foehn is usually a light southerly flow (Waedenswil might have moderate Foehn winds from time to time).

In the more Foehn-prone alpine valleys the wind direction is - of course - more aligned to the main valley axis, which can deviate quite a bit from south.

There were some very interesting Foehn cases recently, some of the have been documented and described in online reports:

There is a great deal of literature tackling Foehn winds all around the world, some basic information and starting point for personal research is given in our online lexic:

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