SnowFlurry 3 2017/18 | Avalanche warning collective project

A large number of avalanches involving people were reported last week, particularly in the Kitzbühel Alps and neighboring regions. As we were able to gather from the Tyrolean, Bavarian and Salzburg avalanche situation reports, the cause was primarily snow-covered surface frost. The formation of surface frost is difficult to predict accurately. Surface frost is one of a handful of processes for which avalanche warnings are dependent on observations of the terrain in order to be able to localize them well and estimate their influence on the avalanche danger. Avalanche warning is therefore also a collaborative system involving all of us!

Let's briefly discuss the most important points that we normal ski tourers can also include in the bulletin. Basically part of our moral duty:

Rain line

Probably the most important message for estimating snowpack development, especially in fall and early winter. Weak layers tend to develop in the area of rain crusts. In the event of rain on an existing snowpack, a report indicating the height of the rain line and the intensity of the rain is a MUST!

Avalanches, settling noises & crack formation

Nonanet. These are probably the most striking signs of an unstable snowpack. All observed avalanches should be reported to the warning services with altitude and exposure (!). In the case of avalanches involving people but without burials or injuries, always make a negative report by emergency call. (Call the control center: "I would like to report a negative avalanche" - the person on the other end will then ask for more details.)

Surface frost & Nigg effect

In which areas, exposures, altitude ranges did surface frost form before it was snowed in? A special form of surface frost formation is the so-called Nigg effect (named after a Swiss mountain guide). Relatively warm, moist air is brought to a ridge or crest and sweeps over it. If the snow surface on the back of the mountain (usually the shady side) is significantly cooler due to shading or radiation, the water vapor contained in the air is deposited in the immediate ridge area (and only there!) and forms surface frost. This effect occurs more frequently in early and late winter. Anyone who observes surface frost should pass on the information to our joint project, stating the area, altitude and exposure!

SnowFlurry

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Cold to warm

Of the 10 hazard patterns introduced in 2010 by the two Tyrolean avalanche warning experts Rudi Mair and Patrick Nairz, one in particular has found its way into everyday avalanche terminology: Gm.4 or "cold on warm / warm on cold". This pattern describes the following process: if cold, loose powder snow falls on a very warm, usually even moist snow surface, a wafer-thin weak layer forms within a very short time. In the transition area between the old snow surface and the new snow, a huge temperature difference causes angular crystals to form in a confined space (anabolic transformation). These form a toxic and difficult to assess source of danger.

The reverse case, i.e. "warm to cold" (fresh snow at just under 0°C on a much colder old snow surface), can rarely be observed, but has the same effect. If the conditions for such a situation exist, the warning services will issue corresponding information with a request for feedback.

Whether and to what extent a weak layer forms must be determined in the terrain. The altitude limits in the various slope exposures are particularly important (e.g. "Sector South weak layer formation by Gm.4 probably in the altitude range 2500m-2800m, Sector North possible but unlikely in the range around 2000m"). An exact delimitation is only possible if as many winter sports enthusiasts as possible with the appropriate background knowledge look for it in the terrain and report it. You don't need to record a snow profile to do this, just take a close look at the transition from old snow to fresh snow and look for signs of accumulating transformation (wafer-thin, loose, soft, glassy layer). The best way to do this is with an ECT: is there anything happening at the boundary between old snow and fresh snow or not?

Danger pattern "cold on warm". One day after the lower profile was recorded, a slab avalanche was triggered next to it due to this weak layer. The cross shows the location of the profile.

Lukas Ruetz

Zischgeles

Graupel

Graupel forms a weak layer within the snow cover. Intense sleet showers should be reported.

For the particularly interested and persistent: ECT tests

No one needs to record a complete snow profile. Anyone who digs a hole every now and then, gets a quick overview of the different layers (without recording hardness, grain sizes, etc.) and taps an ECT test has two advantages: 1. he gets a feel for what is going on under his boards 2. the result of the ECT helps the joint project with regard to old snow problems immensely. A report along the lines of "ECTP on mountain XY, altitude 2360m, exposure northeast, broken at stroke 23 in the weak layer close to the ground " is worth its weight in gold!

Photos

... say more than a thousand words. Include them in your feedback!

Where to report relevant observations

For example, for Switzerland in the feedback form at https://pro.slf.ch/reply/public/?lang=de or via the White Risk App.

For Tyrol here: https://lawine.tirol.gv.at/service/rueckmeldungen/

Further feedback forms or contact addresses of other institutions can be found on their websites.

Note: In addition to the avalanche transceiver check, another standard measure in the winter mountains is to report relevant observations to the warning services!