Today it will be about mountain weather and more specific about mountain winds. Early morning and a sunny day. The weather service has announced that it is a class one warning over the mountains. I cant see it because the sun is shining and the wind is calm. So we put on the skis and start our trip towards Helags mountain station. After six kilometers the shit hits the fan. We got wind and snow from ahead, and it begun to get cold. This is how it normally looks like in the mountains. So now I will show you a bit more of how wind arises and occurs in highland terrain. it is based on the image below.
A nice day in the mountains, the sun is shining and its nice. But the weather can suddenly changes and then it is good to keep an eye on the wind’s effect on weather and trail conditions and possible protection, bivouacking. So let’s begin with winds in valleys in the mountains.
Winds in walleyes in the mountains. The winds in a Walley means they have to pass a narrow passages. This means it will be affected of the venturi effect. This means that (see picture and no1.) the wind due to the venturi effect in combination with the air pressure will increase the wind speed from 10 m/s up to 17 m/s. And it will of course have very different impact in which direction you are going.
The next phenomena will be the corner effect. This can be comparable to the effect you probably have experienced at the sea, when you pass a corner the wind will affect you. It will follows the terrain and will be extra strong in the corner. (Helags mountain is a good example of his).
If there is a wind in the top of the mountains and you have winds going upwards as you can se in picture 3, you got a so called corkscrew effect. This will have a certain effect for the air traffic in the mountains.
You also got an effect like a foen(blow) wind.(se figure 4 in the picture) You have a inversion up to the first level, and little wind. You got hot air flowing upside. When it passe a high peak the air will fall down and it will be warm down below. In 2016 the temperature in January was measured to 14,4 Celsius.
When the wind blows straight towards a mountain, you can get a so called blocking effect. If the air cant go over a big mountain the air will accumulate and related to the pressure gradient of the air pressure the air will go on to that side where the pressure is lowest. (fig. 2a) If it is a lower mountain the wind can pass over it.(fig. 2b)
A dangerous situation can appear when there have been a high pressure under a longer time with cold temperature. This in combination with stagnant air, and a air pressure gradient. This will make the wind to increase. A significant sign of this is snow drift on the peaks. This will be a clear warning sign if you are in the mountains. In the foot of the mountains the weather can be nice and no winds, but you can see plumes or snow drift on the tops. This is called katabatic winds and was one of the Cause of the Anaris incident.
Ok, so what will be the conclusion out of all of this?
First of all listen and check the weather report, ask locals about how the weather has been last week. If you are going to pass a valley, check the wind direction. It can be a wind tunnel trap. If it is windy avoid ”corners” where the wind can get different directions. If you have the wind from back and you moving to a high mountain, the wind can in a sudden turn fast near the foot of the mountain(the blocking effect) And if it has been a high pressure with real cold weather for a longer period and you see plums/snow smoke at the peaks, it can be real windy at the foot of a mountain with raging winds down. This meaning to avoid valleys, streams and furrows where the wind can gain extra speed. And especially don’t build bivouacs or emergency shelter in that type of area. And maybe most important of all, normally the wind under the three line don’t get over 10m/s which means that if its possible always have a evacuation way downwards to the tree line…And don’t forget that it will blow 30-50% more on the peaks comparing to the free atmosphere around it.
This week I have reviewed the Snigel Field Binder. This is the perfect travel partner for administration. Maps, tickets etc. It has two big pockets for maps, and a lot of pockets for other stuff. A holder for light and also a lot of holder for pens. I really like this, but it will only get NNNN(+) the reason for not get a 5 is that it is to expensive. It cos about 86 Euro (~850:-)
In 2022 it has been 72 blogs for all you who have read them:-) Sometimes I feel I write about the same, but comparing to ex. Utemagasinet with 12 releases I don’t think I have to worry…Hope you all have enjoy it:-)
See ya soon…