Second warmest winter in history
The meteorological winter 2019/2020 (01.12 - 29.02) is coming to an end. According to ZAMG Weather Service it is the second warmest winter in the 253-year history of measurement-taking. One measurement stands out: at Innsbruck Airport on 23 February in the evening the temperature was 20.5°C. (Only twice was this temperature exceeded in a meteorological winter: on 24.2.2008 and on 28.2.2019, when 20.6°C was reached).
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| According to Alexanderr Radlherr from ZAMG Weather Service: extraordinary, over 20° in the evening, wind-adjusted mixture of air masses without sun. |
Storm winds once again
The ZAMG Weather Service warns of a short but intensive storm-low which will move over Tirol today and tomorrow (27-28.2). The northern rim of the Alps will be hardest hit. In the latter part of the night, the storm winds will slacken off from west to east, easing further on Friday morning.
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| Easily recognized: winds intensified significantly during the daytime. Simultaneously, snow depths decreased noticeably. Thus, snow was transported. |
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| Maximum wind gusts |
Fresh snow, again and again
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| Several times last week there was precipitation. Here the fresh snow from 26-27.2 is visible. Today (27.2) more fresh snow will be added to it. Most of it in the western regions (up to 30 cm, locally more). |
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| Forecast of fresh snow for the next two days |
Main danger stems from fresh snowdrifts
The combination of fresh snow, wind/storm plus cold temperatures inevitably leads to wide-ranging snow transport.
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| Snow plumes indicate snow transport. Silvretta (photo: 26.02.2020) |
The snowdrifts which were generated and occur in very steep terrain at high altitudes are increasingly prone to triggering, especially behind abrupt changes in the terrain and on shady slopes. A potential weak layer for slab avalanches is found inside the mass of fresh snow, e.g. graupel, possibly also cold loose powder. In addition there is currently a layer of decomposed snow beneath thin crusts near the snowpack surface, above the treeline. Also there, in case of a deeper layer of fresh snow and drifts, a fracture is possible by appropriate loading, e.g. the weight of one sole skier. Avalanches show no great risk of great magnitude due to little fracture propagation tendency (medium-sized at most). In addition, in very isolated cases older layers of faceted crystals beneath crusts (above 2300 m on shady slopes) are prone to triggering.
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| Soft layers beneath crusts can be a weak layer for slab avalanches when snowdrifted masses are deposited atop them. |
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| A similar situation in the profile above. In addition, there is here a further weak layer in the form of faceted crystals which seldom occurs, from the end of January. The last layer can be triggered only by large additional loading where snow is shallow. |
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| Indicative of sunny terrain: stable layering with a sequence of crusts and and a snowpack riddled with melt-water canals. |
The snowpack surface
What matters in this connection is the extremely irregular snowpack surface with which fresh snow and drifts have in generally bonded rather well.
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| Snowpack surface heavily wind-impacted. East Tirolean Tauern (photo: 22.02.2020) |
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| Avalanche deposits from 03-04.02 in the Silvretta. (photo: 18.02.2020) |
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| Breakable melt-freeze crusts in sunny terrain on the Main Tauern Ridge (photo: 22.02.2020) |
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| Really loose, cold powder was rare. Mostly it suffered impact from wind and solar radiation. Tonigenkogel (photo: 22.02.2020) |
Striking on 23-24.02 was that rain fell up to high altitudes. At intermediate altitudes the snowpack was thoroughly wet, 0° everywhere. Subsequently during a star-studded night the snowpack surface formed a solid melt-freeze crust.
Last week’s weather: warm, variable, windy. Rainfall up to high altitudes.
Last weekend and at the beginning of the week, a westerly air current brought very mild Atlantic air masses to the Alps. On Saturday, 22.2 the air was still dry, supplying us with ample sunshine and a few harmless cirrus clouds. As Sunday approached the air became moister, a few compact cloudbanks dominated. On 23.2 in the evening the record-breaking temperatures were recorded. Thereafter it started to rain, extending mostly up to 2500 m, in some places up to 2900 m.
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| Reports of rainfall levels on 23.2 and 24.2 from our observers. |
The westerly air current which prevailed brought a rapid shift from dry to moist air masses on Wednesday, 26.2, then colder air and snowfall. In the course of the day today (Thursday, 27.2) a cold front approached, bringing strong-to-stormy westerly winds and snowfall which are expected to persist until the early hours of Friday. According to ZAMG, the air current will shift to southwesterly next weekend and it will again become milder.
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| Variable: rain on 23.2 and 24.2, subsequently more minor precipitation, windy, good radiation on 24-25.2 due to dry air masses. On 27.2 winds intensifying. |
Situation in the southern regions
The southern regions of the land hardly got any precipitation in the recent period. Only now when the air current is changing is the south getting some snow or rain. What is striking there is the hard snowpack surface, which has caused numerous personal injuries. In one case someone in snowboots on a 30° steep slope slipped, fell a ways and was killed.
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| Indicative of the most recent period: the snowpack surface was frequently icy. Lienz Dolomites (photo: 21.02.2020) |
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| At low and intermediate altitudes there is little to no snow. Sunny slopes are becoming increasingly bare. Southern East Tirol (photo: 22.02.2020) |
More gliding snow for a brief period, generally little avalanche activity recently
Throughout Tirol, particularly in the southern regions, avalanche activity recently has been rare. Most of it came from moist or wet loose-snow avalanches. Increasing avalanche activity was observed in the rain-impacted regions on 24 February in the form of glide-snow avalanches.
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| Glide-snow avalanche in East Tirolean Tauern. (photo: 24.02.2020) |
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| Glide-snow avalanche in Kleinvermunttal. (photo: 25.02.2020) |
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| Don’t underestimate this risk: rooftop avalanches in Defereggental. (photo: 23.02.2020) |
Also to be heeded, observed in isolated cases: breaking cornices.
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| Breaking cornice in the Tux Alps. (photo: 22.02.2020) |
