Main problems: fresh drifts at high altitude, diffuse old-snow threat
The snowdrifts which accumulated over the last week have bonded with each other well, generally speaking. More attentiveness is demanded by freshly generated drifts. These are frequently prone to triggering above about 2400 m, found especially on steep shady slopes and in high-alpine ridgeline terrain. Avalanches are small-to-medium size, for a brief period can be triggered even by minimum additional loading.
The diffuse old-snow problem is more difficult to pinpoint: it occurs at 2400-2900 m in W-N-E aspects, in isolated cases also in SE aspects. Inside the snowpack which has been blanketed since the end of January are thin layers of faceted crystals which can be triggered, most easily on very steep slopes where the snow is shallow and in transitions from deep to shallow snow. Generally, large additional loading is necessary, in isolated cases however, also minimum additional loading could trigger a fracture. Releases can grow to large-sized avalanches.
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| Snow profile at 2870 m, SE aspect, northern Ötztal and Stubai Alps. The arrows point to thin, faceted layers between or beneath crusts. Fractures here propagate inside these weak layers. (photo: 13.02.2020) |
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| Profile similar to the one above (rear Kaunertal, 2540 m, SE aspect) but in this one no thorough fracture could be generated. |
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| Profile on shady slope, 21 degrees-gradient. In immediate vicinity a settling noise was provoked. Rear Kaunertal. |
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| Large naturally triggered avalanche after 4 February. Sommerwand, about 3000 m. (photo: 08.02.2020) |
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| Large naturally triggered avalanche after 4 February. Kaltenberg, Vorarlberg border. (photo: 08.02.2020) |
Development of Danger Pattern "cold on warm"
As described in the
Blog of 06.02.2020, we are ardently following the development of the rain-impacted snowpack which has been blanketed since 04.02. In the interim there is expansive metamorphosis evident on north-facing slopes beneath a melt-freeze crust which formed starting on 04.02. This potential weak layer has developed in divergent ways. In most cases, a layer of snow on top of it - which would make it dangerous - is still lacking. Nevertheless, if drifts are formed atop it in a narrow altitude band of 2300-2500 m, winter sports enthusiasts could trigger it.
Here are a few profiles of the last few days:
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| Arrow points to thin faceted layer, indicating dp.4 (cold on warm) |
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| Arrow points to thin faceted layer, indicating dp.4 (cold on warm). |
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| Arrow points to thin faceted layer, indicating dp.4 (cold on warm) |
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| The rain crust which formed on 03 February is visible in the photo. East Tirol. (photo: 06.02.2020) |
Heavily wind-impacted snow cover
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| Branches broken and torn by winds are currently found throughout Tirol. (Photo: 13.02.2020) |
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| Winds eroded the snow, but often left old tracks untouched. (photo: 13.02.2020) |
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| Artistic wind sculpture (photo: 12.02.2020) |
Avalanches of the last week
There was an avalanche fatality last week below Murkarspitze (
see Blog).
In another accident on an extremely steep east-facing slope at 2300 m below Grossen Rettenstein in the Kitzbühel Alps, two persons were injured.
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| Avalanche Grosser Rettenstein on 08.02.2020 |
Another
avalanche involving persons occurred on 13 February in Defereggental. No persons were involved.
Weather under the influence of storm-low "Sabine"
Following a weekend of tranquil high-pressure weather conditions and mild temperatures especially at high altitudes, the storm-low “Sabine” reached us on Monday, 10 February.
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| Storm-low "Sabine" |
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| Wind gusts on 10.02.2020 of storm-low "Sabine" |
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| Maximum gusts measured on 10.02.2020 - weather station Elferspitze in Stubaital) |
The stormy W/NW air current brought moist air masses from the Atlantic to Tirol’s mountains with gusts of over 150 km/hr. The storm-strength winds eased during the week. On Thursday, 13 February, a short high-pressure front brought more stable conditions.
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| Initially fine weather, then from 10.02 deteriorating conditions including storm and fresh snow. Most snowfall was in NW regions, e.g. here at weather station Jöchelspitze in Ausserfern. |
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| Storm and resulting snow transport in northern East Tirol (photo: 11.02.2020) |
Outlook
In the wee hours of Friday, 14 February, a front passed through bringing moist, cold air and some fresh snowfall. In the NW barrier cloud regions, ZAMG Weather Service expects about 20 cm of fresh snow, in the rest of Tirol 5-10 cm, less towards southern East Tirol. Snow showers will come to an end during the day on Friday. As the weekend starts, increasing high-pressure weather conditions with sunshine and significantly higher temperatures are anticipated.
Avalanche danger levels will gradually diminish. The diffuse old-snow problem will persist, however. As temperatures rise, increasingly frequent moist-snow slides, possibly also glide-snow avalanches, can be expected.
