Author Topic: The Foehn is blowing in Switzerland  (Read 1706 times)

idunn

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The Foehn is blowing in Switzerland
« on: November 22, 2016, 09:27:16 PM »
Hi Weather Guys

At the moment north of the Alps in Switzerland a strong, warm, south wind is blowing, called a Foehn here. The temperature at 10.40 pm on Sunday here at 900m is about 17C, with the wind gusting to almost 50 km/h. In Basel, 100km to the NW and 700m lower, the temperature is now 7C, with wind gusts of 7 km/h. Just now a gust of 57 km/h blew open a large window.
From my webcam at 7:15, the early morning sky certainly looks like Foehn, with the clear window to the south over the mountains and waves of smooth clouds, although not lens-shaped here. The storm light on the lake was flashing every second.

My WC graph displays average values for T, P, and wind speed. The gusts were up to 50 km/h.

Regions of low pressure move eastwards across Europe with their counter-clockwise winds.  Meeting the Alps, which are oriented east-west, the northerly winds rising over the mountains create rain on the south side and dry warm air to fall down the northern slopes.  This situation is the same as the Chinook winds of the US and Canada. I have borrowed some maps and diagrams from the website of Meteoschweiz, the national weather group here. Hope they don't mind too much. The drawing depicts the Foehn situation. Typical is a region of clear sky, called a Foehn window, caused by the relatively dry air just north of the mountains. Also typical are smooth, lens-shaped clouds, here called Foehn fish.

The isobars over Europe today are shown on the map, with a cold front moving eastwards over
France to Switzerland.  They are fairly close together, indicating large pressure gradients. Apparently the mountains slow the progress of a front, making it difficult to predict, and causing longer periods of Foehn. This one is expected to last a few days.

The rain is shown in the radar map from Meteoschweiz to be very heavy now south of the Alps. I am located at the little lake to the right of the name Luzern.

The north arm of the Lake of Lucerne is particularly windy during Foehn, as the webcam this morning from the town of Brunnen shows. It is located a 30 min drive to the west and about 500m lower. The temperature of 17C is about the same now as here.

The wind map from Meteoschweiz shows the highest southerly winds, over 150 km/h, located over the mountains.

My webcam from 7:45 shows the sky lit by the rising sun, and the Foehn window above the mountains is obvious.

I will continue this on another post, as my attachment limit is 4 

Regards, Irving

Blicj11

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Re: The Foehn is blowing in Switzerland
« Reply #1 on: November 22, 2016, 09:31:21 PM »
Interesting wind development. Thanks for sharing.
Blick


elagache

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Thanks! (Re: The Foehn is blowing in Switzerland)
« Reply #2 on: November 22, 2016, 11:27:59 PM »
Thanks for sharing Irving!

Indeed tall mountains make for some very unique weather!

Cheers, Edouard