Monday 28 January 2013

January weather; inversions and diamond dust

We have had all sorts of weather this January, nothing too hard to cope with but enough to keep us on our toes. We have had a series of good snowfalls, enough to keep the pistes in wonderful condition but not so much that areas have to be closed off while Pisteurs work to make them safe. 

One of the interesting weather events we have had this month not just once but several times is a temperature inversion. Typically as you go up in altitude the temperature falls, the temperature here in Les Allues is usually higher than at the summits. When a temperature inversion occurs the opposite becomes true, the normal decrease in temperature with height switches to the temperature increasing with height. The result is that on the summits it can be much warmer than down in the valley.

In addition to the impact on temperature an inversion can create an interesting cloud effect. Clouds just below the inversion tend to spread out and take on a flattened appearance. When skiing in sunshine it is quite strange to look down the valley and see the where the thick cloud has sunk, almost giving the appearance of glaciers. These pictures do not give the effect full justice but hopefully give you an idea of what happens.







Another curious weather effect we have experienced is diamond dust, again this occurs when the air is coldest near the ground. The result is sparkling flecks in the air which you can feel biting into your skin as you ski through it. Hard to see unless you can get the sun in the right place, if you look carefully at this picture the diamond dust is sparkling in the sunshine.