SnowFlurry 12 2020/21 | First firn then powder on crust

Weather conditions in recent weeks

On 5 and 6 March 2021, a cold front brought some of the eagerly awaited white flakes. On the one hand, the fresh snow came to rest on a thin layer of melted snow in many places, which unfortunately dampened the skiing fun somewhat and made the ascent quite arduous in some places. On the other hand, there were also areas with a snow surface of angular crystals, mainly on shady slopes protected from the wind.

At the end of February (18.2. -26.2. ) and primarily in the first week of March (28.2.-4.3.), not only warm temperatures but also very dry air masses prevailed during the fine weather phases, including perfect night-time radiation. As a result, a layer of melted snow formed on the snow surface on sunny slopes, which also became quite thick at lower altitudes (profile 1). As a result, there was no shortage of spring fun, as there was plenty of firn (slush snow) to enjoy during this time.

The situation was different on the north-facing and shaded slopes. Here, the snow surface was transformed by the good night-time radiation and the resulting strong cooling. This resulted in the formation of small, angular crystals, which were overlaid with fresh snow or drift snow on March 5 and 6, as mentioned above. The layer with angular crystals can cause problems in places where it has been overlaid with a suitable board - for example in drift snow. It still looks as if the danger spots are not very widespread, or that the right board is sometimes missing over the weak layer. But you should keep the angular layer in mind!

In addition, small loose snow slides from steep terrain could be observed more frequently this week.

SnowFlurry

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Some fresh snow: Nice to look at, unfortunately often with a hard base lately — Some fresh snow: beautiful to look at, unfortunately often with a hard base recently

Stefanie Höpperger

Profile 1

See gallery at the end of the article. This profile was taken on 28.2.21, before the snowfall at the beginning of March, at an altitude of 2450m, on a 34° steep southern slope in the Mieminger Gebirge.

It shows an approx. 35cm thick melt crust. Above this is snow that has been softened by heat and solar radiation, including melt molds. The snow cover is isothermal, which means that it has the same temperature throughout, and it is completely soaked. The profile was only recorded at 12:40 pm, but due to the thick snow cover, there is no danger of wet snow, at least at the profile location itself (depending on several factors, of course) and the firn fun should not have been neglected either.

Profile 2

See gallery at the end of the article. This profile was taken on 2.3.21, also before the snowfall at the beginning of March, at an altitude of 2330m, on a 25° steep north-facing slope in the Silvretta.

Here we can see the soft, built-up snow surface of angular crystals lying on a compact snowpack. At the time the photo was taken, this layer posed no danger whatsoever, it was just great for skiing. Only after it was snowed in at the beginning of March did it become a weak layer that could be disturbed. The cold snow surface (-10.6° C!) and the existing temperature difference in the snow cover, which promotes the build-up transformation, are also clearly visible here.

Profile with two recognizable layers of Sahara dust.

Stefanie Höpperger

Profile with two recognizable layers of Sahara dust.

Stefanie Höpperger

Profile 3

Taken on 09.03.21 after the snowfalls of 5 and 6.3.21 in Selltraintal. We are at an altitude of 2364m in a NE exposed, 36° steep slope, which is only very slightly oriented to the east.

On the snow surface you can clearly see the fresh snow from the beginning of March, which is now lying on the built-up converted layers of the fair weather phase. At the profile location, however, the weak layer that is now snowed in is not pronounced enough to cause problems.

The layers:

Violet

This is the precipitation that fell until mid-January and the effect of the accumulating transformation from the cold phase at the beginning of January.

The profile was not shoveled down to the ground (0-50cm) and the layers were not recorded. At this depth, the layers are not relevant at the present time and cannot be disturbed due to the thickness of the snow at this point.

Orange

The snow comes from the precipitation from 14.1. to the beginning of February and the subsequent cold period until 16.2.21. At the border to the layers colored in green you can see Sahara dust deposits from the end of February. (See photo)

Green

Is the snow surface at that time (like profile 2) before the snowfall on 5 and .6.3.21.

Since the profile location is slightly exposed to the east (NE), the sun is already reaching it somewhat, which slowed down the accumulating transformation at that time. This can be recognized by the higher proportion of angular rounded crystals.

The layers originate from the precipitation on 16/17/22 + 27/2/21. 27/27 was the only interruption of the two periods of fine weather, which lasted from 18/2 to 5/3/21. There was also some precipitation on the 27th.

Sahara dust can also be clearly seen in the upper layer of 210-212 cm (see photo)

Yellow

New snow from 5 and 6.3.21

Outlook

From 11 to 12.3, a cold front passed over the northern Alps and brought some new snow, varying regionally from a few centimetres to >30 cm. Depending on the influence of the wind, fresh accumulations of drifting snow formed during the snowfall and on the following day, which are usually rather small but should still be taken into account. A wintry phase with fresh snow and probably quite stormy conditions is on the cards for next week. After a long period with relatively favorable avalanche conditions, things are now getting much more tense again! Weak layers within the fresh snow and the old snow surface (yellow layer profile 3) are likely to be the most critical areas.