Why is there no precipitation in the Alps?


Door meteomorris op 13 november 2015 · 0

November usually brings a lot of precipitation to the Alps. Especially the Southern Alps usually get the base the remainder of the season. Now it's been dry in the Alps for more than two weeks. But why?

High pressure is dominating

Precipitation is necessary for snowfall and exactly that is lacking when a high pressure area is dominating the Alps. Storms never reach the Alps, becasue they have to follow the path that is indicated with the orange arrow below.

Storms stay at a distance
Storms stay at a distance

That high pressure area is changing a little bit every day, but that mainly takes place at the edges of the high pressure area. Because the core of the high pressure remains located in the same spot above the Alps, they don't notice a thing about the changes at the edges. They're looking at blue skies in the Alps for days.

You can also spot that orange arrow almost identical as the one above on the the map below. The orange line is the jetstream, that functions as a highway for storm depressions. If the jet stream isn't situated above the Alps, chances for freshies diminish rapidly.

The jet stream
The jet stream

But it is also relatively warm in the Alps

The jet stream separates cold air from the north from warm subtropical air from the south. If the jet stream is located north of the Alps (as it was in the last two weeks), it is relatively warm in the Alps. If it is located south of the Alps, as in the map below, it is colder. Thus, the heat is the result of a jet stream which is located too far north, the fact that there is no precipitation is the result of the dominant high pressure.

The jet stream is the green river
The jet stream is the green river

But why does it take so long?

That's a good question. Such high pressure blockages, in which a high-pressure area stays at the same location for a long time and forces storm depressions to follow a detour, are still largely a mystery to meteorologists. Both the occurrence and the eventual disappearance of it prove to be very difficult to predict for the different weather models. Fortunately, there is one certainty. Eventually they make way for the storms. It will snow eventually. And the even better news is that an increasing number of parameters calculate the end of the drought.


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