Snow for the southern Alps! Will it snow in the French Alps as well?


By meteomorris on 9 October 2016 · 2

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!

Grossglockner
Grossglockner

Autumn in France
Autumn in France

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.

Negative NAO

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.

TIP: check out this article about the NAO and the influence on winter in the Alps

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.

NAO index negative
NAO index negative

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.

Phases in the jetstream
Phases in the jetstream

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.

Snowfall at the Stelvio
Snowfall at the Stelvio

Snow above St. Moritz
Snow above St. Moritz

Look closely, the first flakes at the Hossa Bar
Look closely, the first flakes at the Hossa Bar

Check out the 23rd of September 2015. That was quite a diffence.

23rd of September 2015!
23rd of September 2015!

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.

TIP: Check out our detailed snow maps of the Alps here

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.

Stay stoked!

Comments


  • thomasweller
    Tourist
    thomasweller op 10 October 2016 · 10:24
    Along with a negative NAO we're currently experiencing a (record) negative AO (Artic Oscillation). You all may remember that last year's disasterous start to the season was in great part due to a record POSTIVE AO where all that cold air kept spinning in nearly perfect circle over the Artic until finally in mid-January that end and we got the cold air wobbling down south.

    Here's the website for where argueably the world's most expert scientist of the AO, Dr. Judah Cohan, updates his AO reports. https://www.aer.com/science-research/climate-weather/arctic-oscillatio...

    He also keeps you up to date about NAO.
    Hope that helps any other weather-nerds like me out there! Early signs bode well for snow in southern Alps this Fall...and the Siberian snow cover which is at it's greatest since taking measurements in '97.
    Thomas
  • Chester_Tartsnatcher
    Expert
    Chester_Tartsnatcher op 10 October 2016 · 16:30
    Epitech discussion there. Forecast is not so good for N. American west. May it dump in the Alps.

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