SNOWvember: the how and why of the huge snowfall


Door meteomorris op 20 november 2019 · 0

Record amounts of snow, spontaneous avalanches, households without electricity and ski areas that open earlier than planned. What is the story behind SNOWvember 2019?

Since the beginning of November, storm depressions have been coming and going towards the southern side of the Alps. Various depressions traveled from the Atlantic to France via the Mediterranean. Relatively cold air and lots of moisture were transported to the south. To the west of these depressions the cold air was brought in with a northern current, while to the east of the depressions this cold and moist air was pressed against the southern side of the Alps with a very strong southern current. The result was huge amounts of snow, regularly to very low on the mountain and from time to time even passed the main alpine ridge.

The fact that several low-pressure areas are entering the Mediterranean is not so strange during this period of the year. It is even typical of autumn when cold air from the north mixes with the still warm air above the Mediterranean Sea. But looking back at the weather in the past 20 days, the following things stand out:

  • Huge amounts of snow
  • Also lots of snow lower on the mountain
  • A long-term stationary situation
  • With snow from time to time far beyond the main alpine ridge

Huge amounts of snow

The amount of snow that fell the last 20 days is striking. Let me start with some images from west to east. The entire southern Alps had to handle a lot of snow. From the French Southern Alps, via the Italian Piedmont to Sella Nevea in the east. There is now a lot of snow everywhere.

Pelvoux (c)Rogier van Rijn
Pelvoux (c)Rogier van Rijn
Bosco Gurin
Bosco Gurin
St. Moritz
St. Moritz
Cortina d'Ampezzo
Cortina d'Ampezzo
Sillian
Sillian

Particularly striking are the amounts of snow in the southeastern Alps where the snow cover is already more than 3 meters thick on a number of peaks. But it is also unusual that at the end of November south of the main alpine ridge that we have a snow cover that is one and a half to two meters thick over 2000 meters .

(c)ZAMG
(c)ZAMG

We see the same picture in the Swiss main alpine ridge and the areas south of it. There too, a snow cover that quickly becomes 1 meter thick (or more). Mind you, we are talking about a snow cover.

TIP: check out this article about the discussion about centimeters.

A lot of snow that has fallen everywhere in the southern Alps. We have regularly seen November pass with a lot of snow on the south side, but often this was fairly local. Now the entire southern Alps are provided with a thick layer of snow and the base has been laid for the rest of the winter.

Also lots of snow lower on the mountain

A special feature of the current SNOWvember is not only the spread of snowfall in the entire southern Alps, but also the often very low snow line. A November with a lot of snow in the high alpine is not exceptional. Who remembers November 2014 when locally 5 meters of fresh snow fell? Lots of snow in the high alpine, lots of rain in the valleys. It is not unknown in November on the southern side of the Alps, but that is a lot of snow in the mid-alpine. The amounts of snow in the mid-alpine locally exceed (or approach) the records for this time of year. Some examples:

  • Simplon Dorf (1470 m, VS): 103 cm
  • Bosco Gurin (1525 m, TI): 102 cm
  • Göscheneralp (1550 m, UR): 99 cm
  • Ulrichen (1375 m, VS): 96 cm
  • Maloja (1810 m, GR): 96 cm
  • Pinzolo (1775 m. TR): 144 cm
  • Nassfeld (1569 m, CA): 93 cm
  • Zettersfeld (1903 m, Tirol): 140 cm

Whether all the snow in the mid-alpine will make it to winter is questionable. It is only November and rain is not rare until mid-January on this part of the mountain. We're going to see it, but a lot has to be done to completely wash away such a thick snow cover and I don't see that happening so quickly.

A long-term stationary situation

We owe this important snowfall to a so-called blocking situation in the atmosphere. This means that the centers of high and low pressure do not move or do not move much. In the past two weeks, a huge high-pressure area between Eastern Europe and Russia has prevented a "normal" circulation of depression from west to east. This forced them to follow a north-south course. The cold air could feed on the mild moist air of the Mediterranean sea and gain some extra energy. The collision against the wall of the southern side of the Alps did the rest. As a result, in recent weeks we have mainly seen this type of maps with storm depressions on the southern side of the Alps.

Cold air sinks with a northern current via the west and is pressed against the Alps with a southern current east of the storm. We see that more often during this period of the year, but its duration is exceptional. To make this clear a next map. Where the jet stream usually goes from west to east and we mainly see low pressure in the north and high pressure in the south, this is now completely different. The map below shows the air pressure deviations at altitude relative to the standard (average situation in the same period of the year) calculated over 30 years (1981-2010). The pressure is remarkably high compared to the average for Russia and the Atlantic Ocean, while this is abnormally low for Western Europe.

The explanation for the prolonged intense period of snow is in the pressure distribution above. Something that is highly exceptional and that deviates from what is normal.

With snow from time to time far beyond the main alpine ridge

Lots of snow in the entire southern Alps and up to the mid-alpine. A fourth peculiarity was the way the snow covered the main alpine ridge from time to time. This is due to the dynamic current at high altitudes which allowed the precipitation to spread further north into the internal valleys such as Zermatt, the Conches Valley, the Engadine, the Ötztal, Stubaital, the Hohe Tauern and even beyond the border between Carinthia and the Salzburgerland.

We are going to benefit from SNOWvember 2019 for the rest of the winter. Especially since another Genoa-low follows in the weekend of November 23rd.

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