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SnowFlurry

SnowFlurry 5 2021/22 | Flockdown

Snow profile discussion

by Stefanie Höpperger • 01/08/2022
First rain up to high altitudes, then several days with warmer than average temperatures for the time of year, and then the long-awaited fresh snow finally fell from the sky.

Review:

The period of fairly modest snow conditions began on 12.12. and lasted until 5.1.

The warm front, which visited us on 12.12. with light rain up to around 2000-2300m (Tyrol), moistened the snow surface. With the cold temperatures and clear nights that followed, a cover formed on the snow surface. On December 14, a period of fine weather began with clear nights and dry air, during which the snow surface cooled down considerably. On 21 and 22 December, a snow surface temperature of -20°C was measured at the Kühtai Längental measuring station.

Phases of fine weather with clear nights promote the accumulating transformation enormously and the energy exchange with the atmosphere takes place not only at night but also during the day. The drier the air and colder the temperatures, the more the snow surface is cooled. In addition, the wind also cools the snow surface somewhat.

These processes resulted in a large temperature difference in the layers near the surface, which set the process of anabolic transformation in motion. Angular crystals formed again and the snow surface became increasingly loose again on shaded slopes. In areas protected from the wind, a snow surface of loose, angular crystals, also known as nap powder, could be found, usually alternating with broken snow.

In addition, surface frost was formed in many places due to the build-up transformation on the surface (deposition). High fog, which prevailed for several days from December 16, intensified the formation of surface frost and huge frost crystals could sometimes be observed.

On December 29/30, the next warm front hit us. At first it brought snowfall, but as temperatures rose, so did the rain line in some areas up to around 2500m. This was followed by several days with spring-like temperatures that were too warm for this time of year. No wonder that many people got their climbing gear out again to climb a few more pitches on the pleasantly warm rock! The conditions for ski tours deteriorated rapidly due to the rain.

The rain on 29/30 December and the very warm temperatures up to 5 December had one huge advantage, however, as the previously extensive surface frost and loose snow surface was destroyed, at least at low altitudes! If these layers were covered by fresh snow, they would form an extremely toxic weak layer. So at least the conditions in the forest area - even after the fresh snow - remain quite avalanche-safe.

On January 5, the time had come, a cold front brought lots of white flakes!!! Fresh snow at last! What was interesting was that when the snow started to fall, the wind died down briefly and then picked up again. This created different layers in the fresh snow pack, as you can see from the snow profile. Above the tree line, cold drift snow packs formed that are easy to disturb.

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About the profile:

The profile was recorded on 05.01.2022 at 13:20, at an altitude of 2146m, on a 32° steep, east-facing slope. All layers are dry (1).

Green:

0 - 27 cm: angular-rounded crystals with a size of 1 - 2 mm and a hardness of 3 (one finger)

27 - 28 cm: angular-rounded crystals with deep rims, a size of 1 - 2.5 mm and a hardness of 2 (four fingers). These are large crystals with clear facets that are again in the process of decomposition. Their corners and edges become rounder again, the crystals smaller, which has a positive effect on the stability of the snow cover.

The layers originate from the snowfalls until the end of November.

Grey:

28 - 29 cm: Melt crust of angular-rounded crystals, with a size of 1 - 1.5 mm. With a hardness of 3 (one finger), it is a fairly soft crust. This is due to the fact that it has already been "eaten away" somewhat. It was formed by the rainfall and heat from 30.11./1.12.

Red:

This is the precipitate from the beginning of December.

29 - 49 cm: angular-rounded crystals with a deep hoop, a size of 1 - 2.5 mm and a hardness of 2 (four fingers). These are also large, multi-faceted crystals that are in the process of decomposition.

49 - 52 cm: a fairly compact layer of 0.5 mm small, angular-rounded crystals with a hardness of 3 (one finger).

52 - 68 cm: another somewhat softer layer (hardness 2) of small, angular, rounded crystals.

Light yellow:

68 - 71.8 cm: a layer of angular, loose crystals has formed below the ice lamella, which is already back in the decomposing transformation.

0.5 mm small, angular crystals, some of which already have slightly rounded corners and edges, with a hardness of 1-2 (fist - four fingers).

Above this, from 71.8 - 72 cm, there is a wafer-thin ice lamella, formed by the rainfall on 29/30 December. The rainwater seeped into the snowpack and accumulated on the colder layers below, where it then froze again.

Yellow:

72 - 73 cm: a thin, loose layer of small, angular crystals has formed between the ice lamella and the melt crust. The melt crust (purple) was the snow surface before the snowfall on January 5. This cooled down considerably due to the radiation as described above, resulting in a large temperature difference in the upper layers of the snow cover, which set the build-up transformation in motion.

Violet:

73 - 75 cm: Melt crust made of melt forms, with a size of 1 - 2.5 mm and a hardness of 3 - 4 (1 finger pencil). Rain crust from 29/30.12.

Blue:

75 - 94 cm: this is the fresh snow from 5.1.2022.

You can clearly see from the different layers that it initially snowed without wind: loose fresh snow crystals with a hardness of 1 (fist).

On top of this is a wind-worked, bonded layer of felted sticks mixed with small, round crystals with a hardness of 2 (4 fingers).

On the surface there is again a loose, only slightly bonded layer of fresh snow and felted crystals, again with a hardness of 1 (fist).

In the extended column test, two partial fractures were obtained. In each case in the thin, angular layer between the fusion crust (purple) and the ice lamella.

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This article has been automatically translated by DeepL with subsequent editing. If you notice any spelling or grammatical errors or if the translation has lost its meaning, please write an e-mail to the editors.

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