Diffuse radiation raises likelihood of triggering on shady slopes - Caution urged esp. at 2200-2600m
As was amply evident in the most recent blogs, it was possible to savor superb powder snow in many areas on shady slopes amid low temperatures last week. As of today, 19.04, the sun appeared frequently between the clouds. This, in turn, led to heightened diffuse radiation impact, and on the other hand, to a superficial bonding of the powder snow to the snowpack. In a nutshell: a slab formed.
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| View from Seegrube towards the south. In afternoon, mostly scattered clouds and a bit of sunshine. |
Slab avalanches can always release when there is a weak layer and a slab. A weak layer with good fracture propagation can currently be found on north-facing slopes in a narrow altitude band of 2200-2600m. There, at the beginning of April due to rain impact, a thin melt-freeze crust formed. This was generated atop a thin layer of faceted crystals, ergo, the potential weak layer.
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| Naturally triggered slab avalanche below Sommerwand in the Stubai Alps. North, 2400m. Time of release: 19.04.2021, 1:15 pm |
Caution urged esp. in regions in North Tirol where there has recently been heavy snowfall
This applies to North Tirol and there, to the regions where there was the most snowfall between 12.04 and 13.04. To be precise: Tux, northern Zillertal, eastern Stubai and Ötztal Alps, Karwendel, Mieming Massif.
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| 24-hr-snow differences from 12.04. to 13.04.2021 |
Our estimate is based on reports and observations received today (19.04). We received reports of naturally triggered slab avalanches in Stubai and Zillertal Alps during the afternoon in this altitude band. Initially, we assume heightened proneness to triggering of the snowpack there.
Also on sunny slopes: a treacherous situation from place to place
Depending on radiation impact and daytime warmth, even sunny slopes could be more prone to triggering tomorrow (20.04) in the regions referred to above and in southern East Tirol. Over the coming weekend, with fine weather and increasing temperatures forecast, it promises to become exciting on sunny slopes. We will report more on this on Thursday, 22.04.2021 at latest.
