Weather models not yet convincing for a PA#2


By Henri on 7 December 2022 · 0

Too good to be true?
Too good to be true?

With our optimistic forecast map, it would be time for a second Powder Alert now, but I am still cautious. Especially now that this evening's new model runs confirm that it is going to be tricky. Snow is going to fall, but for the Eastern Alps this weekend probably less than seemed possible in recent days, and significantly less than our model is showing today.

In this weather report:

  • A brief recap of today
  • Snow in the French Alps, then the Southeast Alps
  • Then the Eastern Alps and the north side, or not?

Short recap: some snow showers today in the Northern Alps

In the vast majority of the Alps, it was a sunny day. Only the northern Alps still had to deal with a tail of a cold front to the east of the Alps. Especially in the northern areas, it still snowed lightly in the morning, but it gave only a dusting of snow. The more inner-Alpine areas just stayed dry and from the west the sun came through in more and more places.

Approaching low pressure area provides precipitation for the French Alps Thursday night (wetter3.de, DWD)
Approaching low pressure area provides precipitation for the French Alps Thursday night (wetter3.de, DWD)

Snow in the French Alps

Our focus, however, is on the upcoming snowfall. The French Alps are first up. Tomorrow, a depression from the Atlantic will approach and bring the first snowfall tomorrow evening in the French southern Alps. With the snow, expect wind speeds higher up to around 100 km/h. Most of the snow will fall overnight into Friday and Friday morning. The depression does pushes a portion of warm air towards the Alps, so we will see the snowline rise quite a bit, on the southern side to temporarily 2,200 metres. Inneralpine and especially in the French Northern Alps, the cold can maintain a bit better, but here the precipitation amounts are also lower. The snowline here also temporarily reaches above 1500 metres, but drops steadily again during Friday.

Around 20 to 30 centimetres of snow could fall in most places, higher up in the Écrins and south also significantly more. Some higher-resolution models here hint at (well over) half a metre of snow in the high mountains. With the rather high snowline in the south and thus heavy snow up into the high mountains, it's just not ideal.

Also some snow for the Southeast Alps

Not only the French Alps will get some of this snowfall, as the precipitation area moves further along the alpine southern edge towards the Southeastern Alps. Some 10 to maximum 20 centimetres of snow could fall in the southern areas on Friday, more in the Julian Alps, but also with a rising snowline to around 1,800 metres. On the northern side, although colder, snow will not reach much further than central Switzerland.

Vb-like low passing (wetter3.de, DWD)
Vb-like low passing (wetter3.de, DWD)

Then snow for the rest of the Alps?

Behind it, however, another depression from the Mediterranean follows more or less a Vb-route towards Poland/Ukraine, with a possibly slightly too wide a turn around the Alps. You can read what a Vb low pressure area is in this article. Usually we can see some nice surprises with a "Vb-Wetterlage", both in the eastern south and north sides, but probably not this time. However, it does seem that considerably colder air will be transported to the northern and western Alps on the backside of this low-pressure area.

What can we expect? To answer the question in the caption of our snowfall forecast in the beginning of this weather forecast, I really think our snowfall map is way too positive today. The other weather models show a different picture. On Saturday, precipitation intensity increases on the northern side and eastern southern side of the Alps. Until Sunday morning, we are still talking about some 10 to maximum 20 centimetres of snow, but especially in the eastern stau areas of Austria, it could still snow on Sunday with a snowline down into most valleys. Over the weekend, high-pressure influence from the west increases significantly, ceasing the snowfall. Also in Tirol and Vorarlberg, it looks like it will slowly clear up as early as Sunday. With some luck, the areas in the Salzburgerland region could still get quite a bit, but the course of the low pressure core has to be right.

ECMWF runs of this morning's 00z and tonight's 12z with expected precipitation amounts through Monday night (wxcharts.com)

So these amounts are not completely certain yet, but the trend in the models is negative rather than positive at the moment. Most of the snow now seems to end up further northeast of the Alps because the core of the low-pressure area is calculated too far east. The course of such a Vb-like low pressure area is still difficult to determine, especially at this timeframe. Do you want to ride powder? Then look in the areas where the base is already good. Nassfeld, for example, seems suitable at the moment with around 20 to 30 centimetres of snow over the weekend with a falling snowline over the course of the weekend. In other areas on the northern side of the Alps, some touring and offpiste line will also be possible, but you have to keep in mind that the snow cover is simply still very thin in most places and snow amounts this weekend could be disappointing. A thin snow cover however doesn't mean that there is no avalanche danger. Check this video made by the avalanche warning service of Tyrol:

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