SnowFlurry 13 2020/21 | Powder: Not all that glitters is dust

Weather development

Circa from 10.3.21, the wind paid us a visit once again, causing the loose snow surface at that time to be displaced and fresh drift snow packs to form, which sometimes came to rest on loose layers on shady slopes.

On 14.3.21, a north-westerly storm marched in and brought stormy winds from the north-west and some precipitation. New snow packs formed. Due to low temperatures and further precipitation including wind, the problem persisted and the avalanche danger even rose to four on the five-digit scale in the main low-snow areas on March 16 and 17, 2021. Furthermore, fresh drift snow packs were overlaid in places by looser layers of fresh snow - which fell without wind - and were therefore difficult to recognize. This made the situation somewhat treacherous, as many danger spots were no longer visible in the terrain. It was mainly the loose powder on the surface that was noticed, as this is of course always very tempting!

Weak layers included loose layers between crusts, weak layers close to the ground, loose fresh snow crystals and the loose snow surface that was present before March 14. So there was also a slight old snow problem in addition to the drift and new snow problem.

The fluffy new snow surface and the fantastic powder fun didn't exactly make it easy to hold back. Even if a drifting snow problem is not as treacherous as an old snow problem, you should still pay attention to the situation report and consistently avoid certain areas.

With the start of the fine weather phase from 23.3.21, the drifting snow problem increasingly calmed down, the snow quality for skiing unfortunately also deteriorated due to the warming.

SnowFlurry

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Cornices show us the wind direction — Pikes show us the wind direction

Stefanie Höpperger

What to look out for in the event of a drifting snow problem

Wind signs: Cornices

Cornices are good signs of wind drifting, especially near the crest. They allow you to see where the wind has carried the snow and deposited it as drift snow.

The lee side is where the overhanging roof of the cornice is located - this is where the transported snow was deposited. The cornice shows us the wind direction: The wind was blowing in the direction in which the cornice is overhanging.

The windward side points against the wind direction. There are blown-off, partially exposed areas, as well as the flat side of the cornice.

A little mnemonic to help you remember which of the two - leeward or windward - is the dangerous side: The leeward area is dangerous because that is where the drift snow lies.

Dunes:

are slight waves on the snow surface and a typical form of deposition of drift snow. The flat side of the dune indicates the windward side, so you can determine the wind direction, but this is not always clearly visible. It is better to avoid these areas.

Gangels and sastrugi:

Gangels are snow forms that remain on the snow surface when the wind "mills" the softer snow out of the surface. It is not a form of deposition, but rather the sometimes quite hard snow structures that remain when the wind has blown away the softer snow. The steep side shows the windward side, i.e. the side facing the wind. The flatter side of the Gangeln is the leeward side. There is no drifting snow problem in the direct area of Gangeln, but it shows us that snow has been transported and also in which direction.

Anraum:

Anraum can often be observed at summit crossings, but also on rocks, plants or other obstacles. The anraut is also an indication of the wind direction. Where it points, the wind came from, so it grows against the wind direction.

Further indications of snow drifting are wind vanes, wind drifting, wind sweeping, etc. If you can observe them, the snow is being freshly transported.

Wind fishing and dunes

Stefanie Höpperger

Optics and perception:

Drift snow often looks a little dull compared to glistening, loose fresh snow.

As the terrain is almost always quite irregularly divided into gullies, crests, hills, hollows, etc., drift snow is often distributed irregularly. As the terrain is almost always quite irregularly divided into gullies, knolls, hollows, etc., drift snow is often distributed accordingly. When making tracks, this can be easily recognized by the different sinking depths.

Bonded snow can be hard, but also soft. Whether snow is bound can be checked with the shovel test, but you can also observe whether a ridge remains standing when making tracks, whether the edges of the tracks are rather "sharp-edged" or whether cracks appear.

Furthermore, drifting snow, especially when it is cold and brittle, feels somewhat dull and "breaking".

The visibility

An emerging drifting snow problem is often associated with bad weather and poor visibility. If the weather forecast for the planned day of the ski tour is already bad, or speaks of clouding, poor visibility and snowfall, you should plan your tour according to the weather. Not only because you can get lost in poor visibility and end up in unsuitable terrain for the avalanche situation, but also because danger signs and drifting snow are difficult to recognize in poor visibility. Even experienced tourers are not immune to this!

A good choice are tours in the forest area, where trees, bushes etc. are available as landmarks for orientation, or tours that you know very well with flatter terrain where there is no danger of getting lost on steep slopes at risk of avalanches, as well as suitable fashion tours where you stay strictly in the main corridor. Of course, the prerequisite is always that you can recognize drift snow in the terrain at all, otherwise it is advisable to stay on the slopes you have seen or to take a mountain guide.

Can you ski a slope despite existing wind signs?

Yes, if the drift snow has bonded well with the old snow cover and there are no other disruptive weak layers, you can ski a slope even if there are still dunes, cornices or similar. How well the drift snow has bonded with the old snow cover must of course be carefully assessed. The situation report provides assistance here. In warm temperatures and sunshine, a drift snow problem can stabilize within a few hours. In cold temperatures and/or bad weather, on the other hand, it can persist for up to several weeks.