The unusually long period of fine weather including extremely low in precipitation came to an end last weekend starting on 25.04. Since then, variable April conditions have reigned, with the long awaited precipitation.
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| Last weekend: ongoing shuffle of sunshine, clouds and precipitation. Griesskogel Group (photo: 27.04.2020) |
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| Precipitation on 28-29 April, most of it in the northwestern regions |
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| Variable weather conditions, repeated bouts of precipitation. Lower temperatures brought a bit of snowfall down to intermediate altitudes. Hahnenkamm station in Ausserfern |
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| A similar situation in northern East Tirol |
Effects on the snowpack
Snow melt continues, slowed down currently by the cool air masses. Thus, generally no snow at low and intermediate altitudes.
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| Down below, no snow. Higher up, little and/or sufficient snow. (photo: 23.04.2020) |
Starting at about 1700 m there is some fresh snow, including a “slight breath of powder” with ascending altitude, according to ambitious backcountry ski tourers. That powder is more or less destroyed (moistened) by diffuse radiation. Beneath the fresh snow (at least below 2500 m) stable summertime corn snow is often found.
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| Stable ‘summer-firn’ in the Stubai Alps (photo: 23.04.2020) |
Persistent weak layers inside the snowpack from mid-winter are unlikely to trigger, conceivable (judged from afar) on very steep shady slopes where the snow is shallow at 2500 to 2800 m. Particularly shady slopes at altitudes around 2700 m snow are in the initial phase of being thoroughly wet, evidenced by simulation models. In high alpine zones (above 3000 m) fresh powder might form a weak layer for a short spell, particularly where there was more snowfall with little wind influence followed by solar radiation bonding the uppermost layer, thus generating a ‘slab’.
Main danger: loose-snow avalanches
Fresh snow reacts very swiftly to the impact of warmth and solar radiation in this season. That means that for a very short time following snowfall, numerous moist/wet loose-snow avalanches can be expected in extremely steep terrain. Precisely that was observed on 30.04 where conditions in outlying terrain resembled a sauna. Slab avalanches and glide-snow avalanches, on the other hand, were rare. In isolated cases small slab avalanches were triggered in the wake of loose-snow avalanches. Glide-snow avalanches have probably released already for the most part. Nevertheless, in rare cases they cannot be ruled out on smooth (mostly grass-covered) ground at high altitudes.
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| Arrows show some of the loose-snow avalanches that released in the Northern Massif above Innsbruck on 30.04. |
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| Nearly all avalanche deposits are from loose-snow avalanches. As a consequence, small slab avalanches were also triggered (encircled). Potential danger stems from cornices breaking. |
More precipitation coming: main danger remains loose-snow avalanches
Here is what the forecasts predict for the next few days: it will remain cool, some snowfall in the mountains (most in the west and along Main Alpine Ridge). Due to a quite stable old snowpack, loose-snow avalanches continue to be the main danger.
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| Forecast of fresh snow and wind in the central Stubai Alps |
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| Fresh snow predictions for the coming days |
A huge debt of thanks
We would like to extend an enormous vote of thanks to all those who have supplied us with so much valuable information over the winter season.
