PA#2 is for the French Alps!

On Monday, I was about to issue a Powderalert, but due to the rising snowline of the past snowfall in combination with the high avalanche risk, I finally decided not to do it. This time, however, with the upcoming snowfall it is time for PA#2! Snow will follow again during Thursday afternoon. You can read all about this snowfall and where to go in this weather report.

Snowline was still low for a very long time

Yesterday’s precipitation in the French Alps and the associated rising temperatures were not too bad yesterday. The expected 20 to 30 centimetres was achieved in most higher elevations, only in Haute Savoie there was a bit less snow than expected. The snowline stayed quite low for a bit longer than expected, but we still saw temperatures climbing to around 0 degrees at 2000 metres later in the day, as shown above here in Beaufortain. The precipitation came a bit further than the models had anticipated. Yesterday afternoon, some light snow even reached Vorarlberg and western Tyrol.

“Luftmassengrenze”

What will follow in the next days? Today we are dealing with the so-called “Luftmassengrenze” I mentioned on Monday. The north-western Alps are in the warm sector. In the valleys, the risk of black ice increases because it is still very cold at the surface, but we are already seeing temperatures above 0 degrees up there. Most of the risk of black ice exists north of the Alps. The more inner-Alpine areas remain almost dry due to the south-föhn conditions. These descending movements dry up the air, leaving most precipitation just north of the Alps. On the northern Alpine edge (e.g. Ostschweiz, Allgäu, Bregenzerwald), the areas should still expect precipitation, which can still be heavy locally. From 1500 to 1800 metres, this precipitation only falls as snow. The small low-pressure core you see here over the Mediterranean Sea is moving further east and will have no impact on the Alps.

Snow from the southwest

Behind it, however, a low pressure area follows from the south-west, which will again bring snow. First of all, it starts snowing in the southwestern Alps during Thursday afternoon. In the French Alps with a somewhat higher snowline (temporarily from 2,000 metres in the south and at the alpine edge, further north and inneralpine lower) than in Piedmont (around 1,500 metres and falling). During the night into Friday, however, some cooler air will flow in again from the northwest, which will also lower the snowline in the French Alps.

Most models expect around 20 to 30 centimetres of snow higher up for Écrins and Oisans and the regions around them. Some models let these snow amounts reach half a metre, but that may still be too optimistic (but certainly not impossible!). At the same time, the precipitation is spreading further towards the eastern Alps, with snow in the Italian Alps and then also on the northern side. I expect around 10-20 cm for the Italian Alps, locally more in the Southeast Alps. For the north side, no more than 5-10 cm may fall in most places on Friday, possibly more in the Stau areas. The snowline here drops into the valleys.

The snowline also rises in the Italian Alps, to around 1500 metres or just above that on Friday. In the Julian Alps even a bit higher. During the night to Saturday, the snowfall remaining in the Eastern Alps will fall with a significantly lower snowline all the way down into the valleys due to colder air flowing in from the northwest.

PA2!

All in all, it is enough for a Powder Alert for parts of the French Alps, especially with the recent snowfall in these regions and because the base here is very good at the moment. However, I would like to add a few comments on this snowfall:

• The avalanche risk is still very high at the moment. Check the avalanche bulletins (link to French Northern and Southern Alps. Also if you are out there in other regions: read the avalanche bulletins! Wind slabs and old snow problems are present throughout the Alps.
• So don’t go out in too steep terrain!
• There is not the same amount of snow everywhere in the French Alps expected. Hotspots are mainly Écrins, Belledonne and Oisans with around 30 to 40 centimetres of snow. Some models also show more, but I cannot say for sure whether that will happen. Our model also gives quite a lot around the Mont Blanc massif, but other models do not follow this!
• The rather high snowline may throw a spanner in the works for some regions. All in all, we can say: too far inner-alpine precipitation amounts decrease, too close to the alpine edge the snowline is higher (temporarily at 2000m). In sheltered valleys, the snowline will likely stay considerably lower.

Friday, the intensity of precipitation decreases. The last snow also falls to well below 1,500m due to the influx of colder air. In the French Northern Alps even 1,000 metres and below. In the evening, increasing high pressure clears from the northwest and the snow moves further east. Saturday will be a day with lots of sunshine in the Western Alps and thus brilliant conditions. From Sunday, it will be considerably milder, especially in the Northern Alps due to the föhn.

Warm south-westerly flow

By the end of the weekend, it now seems fairly certain that the Alps will be caught between a strong low-pressure complex over the Atlantic and a strong high-pressure area over Eastern Europe. In this setting, the Alps will experience a south-westerly high flow with föhn on the north side. Temperatures at 1,500 metres altitude here could possibly reach 10 degrees. It will remain cooler in the southern Alps, though.

Read also:

• What is an ensemble forecast?
• What are low- and high pressure areas?
• What is a northstau/nordstau?
• What is a southstau/südstau?
• What is föhn?
• What is the jet stream?