Review: some snowfall in the mountains, cold, half-week of sunshine
Our weather in the last week has been in the grips of a cold NE air current, bringing snowfall in the mountains, frost in the valleys. The ZAMG Weather Service even registered in the eastern regions a new low-temperature record for 1 April.
One interesting aspect was distribution of precipitation. Focal point: southern East Tirol, but also in the northeastern corner of the northern Stubai Alps.
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| 24-hour precipitation in Tirol on 29-30.3.2020 |
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| Corresponding distribution of fresh snow |
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| Precipitation from 29.3 to 31.3, most in the south, seen here at Thurntaler weather station near Sillian. Precipitation in the mountains fell as fluffy powder snow. As the weekend approached, temperataures were below average, but rising. |
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| Wintery scene near Lienz (photo: 30.03.2020) |
Despite low temperatures, weather was mostly sunny and dry. But feelings of springtime didn’t awaken until 2 April when temperatures started to rise.
Loose-snow avalanches, isolated slab avalanches on shady slopes
The fresh fallen snow was generally quite fluffy. Due to intensive solar radiation typical at this point of the season, loose-snow avalanches are the expected consequence in extremely steep terrain.
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| Deposit of a loose-snow avalanche in Defereggental. The photo was taken by a drone. (photo: 31.03.2020) |
Apart from loose-snow avalanches there were also isolated slab avalanches on shady slopes above 2000 m. Probable cause: a thin, expansively metamorphosed (faceted) layer deposited atop a melt-freeze crust, then blanketed by the latest round of fresh snow. Wherever wind had an impact, the necessary “slab” was able to form. For a brief spell, the fluffy powder had high potential to generate slab avalanches, as always when it is blanketed by fresher snowfall.
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| A naturally triggered slab avalanche photographed from the valley. Schustertal, southern East Tirol. (photo: 31.03.2020) |
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| The large snow deposit at center stems from a slab, the small deposits from loose-snow avalanches. Northern Stubai Alps. (photo: 01.04.2020) |
Below-average snow depths
Following a period of very little precipitation, the overall snow depths have receded further: below average overall depths at high altitudes; at low and intermediate altitudes, if there is any snow on the ground at all, far below average snow depths.
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| Depiction of snow depths from our observation station in Kühtai. Magenta: current values. Heavy gray line: average values. Upper and lower limits show maximum and minimum values. At the present moment: below-average snow depths. |
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| Snow depths far below-average at observation station in Boden, Lechtal |
Outlook: increasingly springlike conditions, with daytime danger cycle
As often mentioned, nocturnal outgoing longwave radiation in springtime is an important factor in snowpack stability for the morning hours of the following day. Webcam photos supply highly important information.
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| Star-studded skies over Kals am Grossglockner. The snowpack softened during the previous day, will have sufficient outgoing radiation during the night. The surface will become encrusted, often capable of bearing loads. |
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| In northern regions, more clouds. Nighttime outgoing longwave radiation is thereby reduced. |
According to ZAMG Weather Service forecasts, the coming days will be increasingly springlike with rising temperatures.
Avalanche danger levels will be subject to a (slight) daytime danger cycle. Danger will frequently be low or moderate. Avalanches will be registered seldom to start with. Isolated moist/wet loose-snow and glide-snow avalanches are possible. On shady slopes, naturally triggered avalanches are no longer likely. Artificial triggerings will be relevant only in very few cases, i.e. due to breaking cornices or rockfall.
Resist the temptation
A fitting complement to the current situation: Article in ORF-Tirol:
