PA#1: Storm Barra gives up to half a metre of snow, more to come on Friday


By Henri on 7 December 2021 · 4

A lot of snow for the Alps in the next 6 days
A lot of snow for the Alps in the next 6 days

Today, a large part of the Northern Alps woke up to yet another layer of fresh snow down into the valleys. Some 5 to 10 centimetres of snow fell, locally up to 20 centimetres. It's a nice preview of what's to come. It's time for the first Powder Alert of the season!

Satellite image this morning (sat24.com)
Satellite image this morning (sat24.com)
Beautiful today in Anzère (pre-opening 8-12 December) (roundshot.com)
Beautiful today in Anzère (pre-opening 8-12 December) (roundshot.com)

Today still dry and later föhn

Storm Barra is approaching the British Isles from the west, but between last night's front and the approaching front that is linked to storm Barra, it can still clear up quite a bit in the Alps. In the Western Alps we have already seen this happen on a large scale due to increasing high pressure influence, but further east in Austria it snowed a bit longer.

Before the occlusion front linked to storm Barra reaches the Alps, the pressure gradient over the Alps increases from the west during the evening. With low pressure north and high pressure south of the Alpine main ridge, a Südföhn situation will develop, see the föhndiagram of Meteocentrale below. Also on the Meteoschweiz wind chart, the föhn is clearly visible around midnight. While the occlusion front with the snowfall already reaches the Western Alps during the night, the föhn will last longer in Austria. The strong southerly flow will be able to move a lot of snow up the mountain and the föhn will be able to break through in the typical föhn valleys. Especially at higher altitudes, it will temporarily become milder, but as the source area in Italy is also quite cold, we should not expect extremely high temperatures. Want to know more about föhn? Then read this article.

Temporary Südföhn conditions this night (meteocentrale.ch)
Temporary Südföhn conditions this night (meteocentrale.ch)
Strong winds in the Föhn valleys this night (meteoschweiz)
Strong winds in the Föhn valleys this night (meteoschweiz)
Storm Barra and a depression over the Mediterranean (wetter3.de, DWD))
Storm Barra and a depression over the Mediterranean (wetter3.de, DWD))

Barra will bring snow

The föhn will be cleared from the west by the approaching occlusion front. Initially the flow will be from the west, but in the course of Wednesday and Thursday it will become more north-westerly. With some persistent stau it may continue to snow in the northwest until Thursday morning, in Austria even longer. On a large scale, 30 to 50 centimetres of snow will fall in the northwestern Alps, but in stau areas like Engelberg and Arlberg I see more than half a metre falling. I think our forecast is a bit too positive for snowfall in Tirol. Other models show around 20 centimetres for this region (except for the areas close to the Arlberg), but the strong southern flow might cause a surprise for the areas close to the alpine main ridge. The snowfall during the frontal passage is again accompanied by strong winds (gusts of 80 km/h higher up). Together with the large amounts of fresh snow, it remains tricky! So keep an eye on the local avalanche reports!

Our snowfall forecast for the next three days
Our snowfall forecast for the next three days

We can see on this map that the Southern Alps are also going to get a lot of fresh snow. This has everything to do with the depression over the Mediterranean Sea and a strong southerly flow that blows a lot of moist air on the Southern Alps. First of all, the French Southern Alps will get 20 to 30 centimetres of snow. Tomorrow, in the course of the day, the precipitation will move further east and the rest of the Southern Alps will receive 20 to 40 centimetres of snow on a large scale with a snowline that will drop to around 500 metres or even lower. Locally in for example the Engadin, the Carnic Alps and the Julian Alps it could be up to half a metre of snow. Inner alpine areas towards Osttirol and Südtirol will receive limited amounts of snow.

Again snow on Friday (wetter3.de, DWD)
Again snow on Friday (wetter3.de, DWD)

Temporary clearing, then snow again

While it continues snowing in Austria on Thursday, it clears up temporarily from the west. This calm phase will only last for a short while, because a new front will arrive from the west on Friday. Again it hits the Western Alps. In France and western Switzerland, 30 to possibly 50 centimetres of snow could fall again by Saturday morning.

Impressive snow amounts until Sunday
Impressive snow amounts until Sunday
High pressure tries to slip towards the Alps (wetter3.de, DWD)
High pressure tries to slip towards the Alps (wetter3.de, DWD)

Over the weekend, the influence of the Azores High expands more and more over Europe. Slowly but surely, the snowfall will be dampened, but a small low pressure core north of the Alps will provide snow in the Northern Alps for a longer time during the weekend. On Saturday, the stau regions of the Northern Alps might see (light) snow for a longer time, especially in Austria. On Sunday, at least the Western Alps seem to have a good chance of sunny spells.

Where to go?

Due to the snowy period of the past few weeks, the base in the north-western Alps is now fine. Please note that higher up it can still be tricky with Triebschnee and with the tricky Altschneelayer. So please keep a close eye on the avalanche bulletins!

To sum up:

  • Wednesday: Dumping in the (North)Westalps, everything east of Arlberg still in the föhn. In the course of the morning/afternoon the snow will also move towards the Dolomites and further east.
  • Thursday: Cloudy with possibly a few clouds in the French Alps and the west of Switzerland, later also a little further east. Sunny in the French Southern Alps. Snowfall persists longer in Tyrol/Salzburgerland. The Southern Alps remain cloudy, but mostly dry (residual snowfall in the Dolomites).
  • Friday: New front arrives in the Western Alps, Austria temporarily sunnier.
  • Weekend: Still uncertain! Saturday and Sunday may be brilliant powder days in the Western Alps, but how much sun there will be is not yet entirely certain. Think for example of some more western ski resorts like La Clusaz, Grand Bornand, Les 7 Laux, Alpe d'Huez. Also in the Southern Alps great conditions.

Later this week more info on Friday's snowfall and where to go for the weekend.

Another snow bomb for the Pyrenees (wxcharts.com)
Another snow bomb for the Pyrenees (wxcharts.com)

Dump for the Pyrenees

A short update for the Pyrenees. In the last two weeks, a lot of snow already fell here, but again a lot of snow is going to fall. The snowfall is again accompanied by a lot of wind, because the jet stream is aimed directly at this region. How much can we expect? Almost all weather models calculate in the northwestern Pyrenees up to 200mm precipitation until Saturday, which means 2 meters of snow! Please note that in the course of Thursday a large portion of mild air will hit the Pyrenees, causing the snowline to rise considerably. In the night from Thursday to Friday, locally above 2000 meters!

Abetone (paesaggidigitali.it)
Abetone (paesaggidigitali.it)

Northern Apennines

The lifts of Monte Cimone and Abetone in the Northern Apennines are already open and there is already a good base. Tomorrow, under the influence of the depression over the Gulf of Genoa, it will also snow here, but in the middle of the day the areas here are just in a somewhat warmer flow so the snow line can temporarily rise to well above 1500 meters. Higher up, some 30 to 40 centimetres may fall, but mainly as fairly heavy snow.

Our snowfall forecast for the Apennines
Our snowfall forecast for the Apennines

The depression that will bring snow on Friday seems to move a bit more to the south, keeping temperatures nice and low and the snow line well below 1000 meters. The models don't show a clear picture yet about the amounts during Friday's snowfall, but 20 to 30 centimetres of fresh snow until Saturday morning is certainly possible with lots of sunshine during the rest of the weekend.

Comments


  • P0WDERP0WER
    P0WDERP0WER op 7 December 2021 · 22:31
    We like that! ❄️ Thank you!
  • 8611
    Tourist
    8611 op 8 December 2021 · 17:43
    Thanks Henri!

    You should put the forecast on the home page and also on Twitter
  • AdamStekl
    Advanced
    AdamStekl op 9 December 2021 · 08:44
    Great forecast. Thank you very much!
    Adam
  • AdamStekl
    Advanced
    AdamStekl op 9 December 2021 · 08:44

    *message edited by AdamStekl op 9 Dec 2021 08:44 (100% bewerkt)
    Adam

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