b'Geek Hub | Engineer Innovation0C10C 15C20C 25CWith the ski season fully underway, Iforced upwards, as the pressure thought this would be a good time todecreases with altitude this causes the turn our attention to mountains,air to expand and cool. As the colder air specifically the effects of weather in theis less able to hold water vapour, the Alps and what causes the warming andwater condenses and forms clouds. drying of air. This is something thatThese then release the water as rain or skiers, snowboarders and residents ofsnow above the mountain. mountainous regions should be familiar with. This can enable us to draw two initial observations, firstly snow is only What I am talking about is the Foehnusually at the top of mountains and (Fhn) effect, which regularly impactsheavier on one side. Additionally weather conditions, not just locally butyou have probably observed a often for hundreds of kilometrescloudless sky on a summers day downwind. Simply, this is a changewith only a few clouds forming from wet and cold conditions on onearound mountain peaks. These side of a mountain to warmer and drierare both due to the pressure and conditions on the other (leeward) side.temperature drop which result in This effect can often lead to massivecloud formation.temperature differences with the greatest being on the 14th January 1972As the clouds form and then in Montana, USA. Within 24 hours theprecipitate the fluid is changing from temperature changed from -48C to 9C,a vapor to a liquid state, this results in this is a temperature increase of 57C! an irreversible heating effect due to the removal of moisture from the air. The While we dont see extremes like this inflow of drier air passes over the the UK, the Foehn effect is mostmountain peak and down the prevalent across the Scottish highlandsleeward side which results in where the high ground along the westwarm dry air. This is a great coast results in wet weather. In contrastexample of atmospheric to this the lower ground across the eastthermodynamics and which of Scotland enjoys warmer weathercan now be demonstrated in with more sunshine. Simcenter Flomaster.How does the Foehn effect work? The image above shows the When air encounters a mountain it iswet air on the left (windward 87'