Lots of snow came down in the main alpine ridge and the east of Austria last week. We could even spot the first skier in Hochkar. It's still in the autumn in the rest of the Alps, but we can't wait for the moment when mother nature really decides it's time for winter!
The atmosphere in the northern hemisphere will change the next couple of months. The days are getting shorter and the polar ice is growing again since September the 10th. The first snow has been observed in Siberia. All signs that it's getting colder in the northern hemisphere. At the same time the water of the Mediterranean Sea, the North Sea and the Atlantic Ocean is still pretty warm and the Indian Summer we're experiencing seems to be unbeatable. It's the time of the year where we have to deal with cold air coming down to the south the one day (like they've experienced in the east of Austria last week), and warm air from northern Africa going to the north. These battles between warm and cold air are pretty amazing and will definitely bring us snow later this season.
The Alps benefit the most from a so-called negative status of the North Atlantic Oscillation. That basically means that the differences in pressure between Iceland in the north and Portugal in the south don't need to be that big. The jet stream will be less powerful and will meander, and the chances are quite high that cold air from the north will go down to the south and will hit mild and humid air above the Mediterranean, resulting in snow for the Alps from time to time.
The NAO is negative right now and you can check the current status every day over here. To give you something as a reference: during the dry autumn of 2015 the NAO index was largely positive, and few flakes fell down in the Alps. Only on [January the 3rd, 2016] (http://wepowder.com/forum/topic/218629) that situation changed with abundant snowfall.
The jet stream is starts to meander during a negative NAO. Check out the three phases of the jet stream below. The jet stream is pretty strong at phase A there. The cold (blue) sky remains above and you don't have to expect any outbreaks to the south. In phase B you can see that the jet stream is no longer that strong and comes in a wave motion. One moment cold air is coming down to the south, the other moment warm air can pentrate to more nothern latitudes. The jet stream meanders the most in phase C. Cold air is traveling to the south.
The first example of that meandering jet stream could be seen last week. Cold air came down from the north and brought snow to Austria. Right now, the cold air is tryin to squeeze itself into the Italian Po Valley, where the temperatures will drop and will bring some freshies. This will result in freshies for the Stelvio Pass, white peaks above St. Moritz and the first snowflakes of the winter season for the Hossa Bar.
Check out the 23rd of September 2015. That was quite a diffence.
The weather will remain unstable on the south side of the Alps the next few days and especially around the Ortler, around the Piz Bernina and the western Piedmont snow will come down above 170o meters. I am more optimistic about the snowfall around the Ortler and the Bernina than our snow maps at the moment. I expect 25-50 centimeters of freshies above 2200 meters. It will also snow in the north east of the Alps on Tuesday.
However, I am still not quite sure of the snowfall in the French Alps that you can see on our snow maps. I see this only on the maps from Thursday and this will be the prelude to warmer air. It will remain cold in the Italian Po Valley due to orographic cooling at first and it will snow above 1500 meters in the Italian Piedmont on Thurday and Friday. The temperatures are already rising on the French side of the Alps. I expect some snow in the southern French Alps with a rising snow line.
But, I'm pretty sure about my forecast till Tuesday. We'll definitely see some peaks getting freshies on the south side of the Alps. What exactly will happen after Wednesday is not certain. Maybe the air will be colder than expected or will the precipitation be more intense. We'll see what will happen next week. It's a fact that winter is getting closer and closer. It will be interesting weeks. How will NAO develop? What will be the influence of La Niña? I hope to answer all those questions the next couple of weeks.