There we go. The meteorological winter has started, now let the weather itself start too. There is no sign of winter in the Alps yet, but it looks like things are about to change. You can expect a lot of snow in the high alpine this week and there is a big chance that the snow will fall into the valleys from next weekend. It will be an interesting week for the northwestern Alps where the snow cover will grow considerably above 2000-2200 meters. Fresh snow will fall deep(er) into the valleys in the northwest and north of the Alps by the end of the week. The rest of the Alps will get almost no fresh snow next week. In this forecast:
November was a great month for the southern Alps. They got a good base during November. There is an excellent base above 1600-2000 meters. That already resulted in PowderAlert #1 and it was ON in the French Southern Alps on Saturday where a number of areas opened their lifts for the first time. But even without lifts and with the help of touring skis and / or splitboards there is plenty to ride in this part of the Alps. It would be nice though if there two more storms bring in some more snow, but you don't have to expect that this week.
The jetstream seems to find its way to the Alps for a longer period of time for the first time this winter. The jetstream is the guide rail on which storm depressions find their way to the Alps. But the jetstream also forms the separation between cold polar air from the north and hot air from the south. When assessing the jetstream, three things are important:
As mentioned, the jet stream is the separation between cold polar air from the north and hot air from the south. If the jet stream is located north of the Alps, then the Alps are located in (too) warm air. If the jetstream is located south of the Alps, it is cold. If the jetstream is right above the Alps, it's all in the details. Warm fronts then provide a rising snow line, cold fronts a dropping snow line.
The direction of the jet stream determines which part of the Alps the fronts will hit. A jetstream from the north brings snow to the southern Alps, from the south to the southern Alps and from the west to the western Alps. And then we also have variants such as southwest, northeast, etc .. In short, the supply direction is crucial.
Cold air can contain less moisture, while mild air is filled with moisture. The combination of temperature and supply direction determine the elevation of the snow line, the part of the Alps where the fronts will hit, but also the amount of moisture. Storms from the south often contain more moisture, so that it can also snow on the other side of the main alpine ridge. Very cold fronts from the north, on the other hand, bring a lot of snow to the pre-Al[ps, but less snow to the resorts deeper in the Alps. They do get a lot of wind in those cases.
The jet stream is therefore an important indicator whether storm depressions come our way. But the location, supply direction and amount of moisture determine the details. But the good news for now: the jetstream finds its way back to the Alps.
And the jetstream provides the supply of a set of storms. At least two storm depressions pass through the Alps between Sunday and Wednesday.
Although the snow maps look good in terms of colors, when you zoom in on our snow maps you can clearly see that the snow will come down in the high alpine first. The contours of the valleys can be clearly seen and it will only snow in the high alpine.
That is not surprising. Although the jet stream is aimed at western Europe, it is too far north. As a result, moisture is pushed from the west-northwest to the Alps. But it is simply too warm. Below you can see the temperature at 850 hPa for Tuesday. It's the temperature in the free atmosphere at about 1400 meters altitude. It is only pretty cold in the very far north of the Alps (blue is cold, yellow is too mild).
Our snow map looks good in short, but those who look on the snow maps and our other maps (temperature, temperature on 850 hPa, clouds etc.) in detail quickly concludes that it is mainly snow for the high alpine.
I am not sorry about that. The high alpine can still use some snow. Snowfall of one meter or more is good as a base for the rest of the season. The high alpine in the northwest and the main alpine ridge of Switzerland and Austria are the ones with significant amounts of snow above 2000-2200 meters until Thursday / Friday. Thanks to #TeamJetstream for the snow dance. Keep it coming!
The meteorological winter has started, but you probably imagine a lower snow line. The snow line is at high elevation until the end of this week. It will be around 2000 meters first and perhaps around 1600 meters later in the week, but that is still on the high side. But the maps really show the start of winter from December 8th for 48 hours now. A depression over Denmark and high pressure over the Atlantic would then have to provide for the classic 'slide'. A slide? It's called a slide because the isobar lines are oriented towards the Alps in the form of a slide. Cold air gets on the slide around Svalbard and then glides full throttle through the jet stream over the North Sea towards the Alps. This cold and humid air hits the Alps and is forced to snow empty. The result? Snowfall deep in the valleys.
You see the shape of the slide above and you can also see that at the temperature on the 850 hpa map below. Cold air then finds its way into the Alps with winter scenes as a result.
Below you can see animation of our weather maps for the expected snowfall between December 8th and 12th. That is a lot. Especially because now the valleys are filled with snow. But those who look closely will see that the snow mainly falls on the northern side of the Alps. The slide usually provides snow in the north and a Föhn on the south side of the Alps.
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But ...... December the 8th is only in 6 days. That is quite a lot in the world of the weather. Especially in the autumn when the dynamics in the models are great. On the other hand, the most important weather models already show this scenario for 48 hours. It is going to be an interesting week. Another update with new analyzes tomorrow .... is winter coming? Let's hope. @ #TeamJetstream... Keep on dancing!
Stay stoked, Morris