007 - Wind

North Foehn

The centre of an anti-cyclone appears in the West of Switzerland. In the same way as happens with the Southern Foehn, when the Nothern Foehn blows the fall in pressure can be very strong in the Alpine region.

Hazards

Aviation

• Clouds coming from the North
• Icy conditions
• More precipitation towards the East
• High winds on the South of the Alps
• Taxing and take-off could be challenging

Road Traffic

• In Winter on the North side of the Alps, it may bring continual snowfall.
• Risk of avalanches.

Tourism

• Clouds coming from the North which can bring continual precipitation, particularly in the East.
• Strong winds in the mountains.
• Lots of snow.
• Risk of avalanches

Westerly Wind

In a jet-stream coming from the West, humid air moves from the Atlantic ocean toward Europe in a circular motion. Following this Westerly current, waves of cold fronts of polar air join to make a depression (unstable, wet weather). They move at a rate of one or two days above Central Europe.

Westerly wind conditions can last for several days, sometimes even a week. They mostly appear during Autumn and Spring. In Switzerland the weather is variable; but more intense in the Northern Alps.

Hazards

Aviation

• Low clouds = poor visibility, turbulence and ice in the clouds.
• In the winter it can bring icy rain in on the warm fronts which causes black ice on the runway.
• A sudden change in wind direction - wind shear.
• Gusts of wind.
• Mountains are generally covered with snow which causes a blinding light to dazzle the pilots.

Road Traffic

• In Winter as the warm front passes there can be heavy snow, which can be sleet at the warm front.
• Heavy gusts of winds as the cold front passes can cause lorrys/trucks to over turn.

Water Sports

• The strong gusts of winds can cause boats to overturn and strong heavy waves.

Tourism/Alpine Sports

• If there are clouds over the mountains it can snow heavily.
• The winds can be strong and storms can occur as the cold front passes.
• After the cold front passes, the temperature can become even cooler which can make things icy.

The Bise

An anti-cyclone appears in the North West or North of Switzerland. Waves of polar air moves from the North above Scandinavia and a zone of low pressure appears above the Mediterranean. When this pressure weakens Switzerland gets a East North-Easterly wind called the Bise.

The distance between the Alps and the Jura gets smaller the further West you go, it is especially so in the Leman region. The air from the North-East is tunnelled between the two mountains. In the lower areas the wind gets faster as it approaches Western Switzerland. In Geneva gusts of wind of more than 50knots have been recorded during the Bise.

Hazards

Aviation

• Strong wind and turbulence in the air closest to the ground.
• Poor visibility under the stratus clouds.
• Holes in the cloud layers can suddenly close.

Traffic

• In Winter the roads can ice over in areas where there is fog or when the rain in the fog refreezes and then falls.

Water Sports

• Strong gusts of winds, especially in Western Switzerland.

South Foehn/Fohn

It is a strong South/South-Westerly current of air coming from above the Alps. In these conditions, the weather map will show similar weather for Northern France, the English Channel and the South of England. The cold front will be moving across France. A small anti-cyclone will form above Northern Italy.

The Foehn wind can last several hours or several days.

The air is humid as it comes from the mediterranean areas on the Southern side of the Alps and the water re-freezes as it passes over the Alps. As the air sinks it warms and the ice melts causing rain. Some people say that this wind causes headaches!

Hazards

Aviation

• On the South side of the Alps, the clouds are low which causes poor visibility, continual precipitation and lots of ice within the clouds.
• During the Summer, storms can occur.
• On the North side of the Alps, turbulence can occur.
• The downward wind can suddenly blow sharply above flat land.

Road Traffic

• Heavy precipitation on the South side of the Alps. In the winter this falls as snow.
• The snow can fall at low elevations causing avalanches and rock falls.

Water Sports

• Strong gusts of wind across the lake.

Tourism/Alpine Sports

• Clouds come from the South and can bring a lot of precipitation.
• Very strong winds especially on the tops of hills it can be fster than 100knots.