Current situation & outlook
April, comes in like a lion, goes out like a lamb.
On the heels of recent springlike temperatures, a low-pressure system over the Gulf of Genoa is bringing back a bout of late winter. In the southern barrier-cloud zones along the border to South Tirol, particularly on the Ötztal Main Ridge, but also in the Carnic Alps, there has been fresh snow registered since evening on Wednesday, 2 April. From place to place in the Timmelsjoch region, as much as 50 cm; in the Dolomites, 20-30 cm. In North Tirol, apart from the Main Alpine Ridge, it remained mostly dry with only light cloud as a result of the strong-to-stormy southerly foehn wind.
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| Especially on the Ötztal Main Ridge, there has been lots of fresh snow registered since Tuesday, 2 April. |
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| Storm-strength southerly foehn wind in North Tirol |
According to ZAMG weather forecasts, the foehn wind will collapse on Thursday evening, 4 April. In its wake will follow a cold front and precipitation, including noticeably dropping temperatures. Particularly along the Main Alpine Ridge and in East Tirol, large amounts of fresh snow are anticipated: 50-100 cm, focal point in the Carnic Alps and on the Ötztal Main Ridge. In North Tirol, rainfall is initially expected to extend up to nearly 2000 m, subsequently the snowfall level will descend down to nearly 1500 m, lower still during the night. In East Tirol, the snowfall level will be 1000-1500 m.
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| Particularly south of the Inn, heavy snowfall until the morning of Friday, 5 April. |
With intensive snowfall and storm-strength winds, avalanche danger will increase. On the Main Alpine Ridge and in East Tirol, danger level 4, HIGH, will be reached. Particularly during the nighttime hours on Thursday and early Friday, large-sized naturally triggered dry-snow slab avalanches are expected in the regions of heaviest precipitation. This applies especially to steep, leeward starting zones on shady slopes and near ridgelines.
Weak layers relevant for avalanches are found primarily inside the fresh fallen snow. The snow which for a short time fell without wind can constitute a weak layer for drifted masses deposited on top of it. In addition, before the snowfall set in there were reports of surface hoar near ridgelines (Nigg Effect), also distant from ridgelines, behind clefts in the terrain, especially on shady slopes. It is even possible that on north-facing slopes, the dry, faceted old snowpack surface constitutes a weak layer. In general, it can be assumed that the snowpack surface before precipitation set in was highly irregular and thus, its structure was essentially favorable. Currently there are no pronounced weak layers inside the old snowpack.
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| Surface hoar resulting from Nigg Effect near ridgeline. Schussgrubenkogel, Stubai Alps. (photo: 02.04.2019). |
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| A limited-spread, highly variable snowpack surface is favorable when fresh snow is on the way. Such snowpack surfaces provide no area-wide weak layer for prospective slab avalanches. Stubai Glacier (photo: 02.04.2019). |
High avalanche danger is primarily applicable to backcountry skiers and freeriders. Transportation routes are unlikely to be endangered by dry-snow slab avalanches. There, it is the glide-snow avalanches and wet-snow slides which matter. Such dangers become relevant in the case of rainfall, especially below the timberline.
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| Temporarily inhospitable winter conditions in Tirol’s mountains. (photo: 01.04.2019). |
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| On Stubai Glacier, the first trigger-sensitive snowdrift accumulations were generated as a result of precipitation-plus-wind. This small slab was triggered on a NE-facing slope at 2200 m. Presumably, the weak layer was surface hoar or the faceted old snowpack surface. (photo: 03.04.2019). |
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| As a result of rain, increasingly frequent glide-snow avalanches are possible. This includes on shady slopes, such as here on Primig in the Lechtal Alps. (photo: 01.04.2019). |
As precipitation comes to an end during the course of Friday morning, 5 April (in eastern regions the snowfall could persist for longer), the wind will slacken off. Thereafter, slab avalanches are unlikely to trigger. However, the wide-ranging snowdrift accumulations, covered in some places, will remain prone to triggering in all aspects. Around midday, the sun will make an appearance again, particularly in the western regions of the land. As a consequence of solar radiation, increasingly frequent small-to-medium loose-snow avalanches can be expected on extremely steep south and west-facing slopes. For a short period, the trigger-sensitivity for slab avalanches can also increase.
On Saturday, beautiful weather is anticipated throughout Tirol. The zero-degree level will ascend to 2800 m. Solar radiation and noticeably higher temperatures will cause lots of small-to-medium wet loose-snow avalanches on extremely steep, sunny slopes. Diverse layers of fresh snow and fresh drifts will swiftly bond with each other, as well as with the old snowpack. Nevertheless, on shady slopes and particularly in high alpine regions in general, these will remain prone to triggering on the weekend. Special caution is urged in shady terrain near ridgelines, where surface hoar might be covered.
After the generally sunny weekend, instable conditions will follow. A new round of perturbances from the south awaits us, although its specific sequence and intensity are still uncertain.
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| Variable weather developments in the coming week (©Meteoblue). |
Review
Last weekend and the beginning of this week were characterized by sunny and mild weather, with little wind. The dry air masses and clear nighttime skies created perfect backcountry touring conditions throughout Tirol.
Over the last few days, humidity gradually increased, nocturnal skies were overcast. Thereby, the snowpack was no longer capable of sufficient outgoing radiation. Warm temperatures and moisture-laden air made the snowpack thoroughly wet even on shady slopes below approximately 2000 m. There, increasingly frequent wet loose-snow avalanches were reported.
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| Measurement data from Obergurgl weather station: from Thursday, 28.03, until Monday, 01.04, nighttime skies were utterly clear. The nocturnal cooling of the snowpack is visible in the gray line. On Monday night, 01.04, on the other hand, the snowpack had inadequate outgoing radiation. As a result of the southerly perturbance, humidity also increased. Since Tuesday evening, skies have been overcast, southerly winds have intensified. Last night and in the early hours of the morning today, 04.04, snowfall set in. |
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| Perfect corn snow could be found on sunny slopes over the last few days. The melt-freeze crust was often more than 20 cm thick as a result of strong nocturnal outgoing radiation, making it capable of bearing loads well into the afternoon. (photo: 28.03.2019). |
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| On shady slopes and where solar radiation was flat, the snowpack surface remained generally dry. There, expansively metamorphosed powder and so-called burled powder or recycled powder could be enjoyed to the fullest. Pflerscher Pinggl, Stubai Alps. (photo: 31.03.2019). |
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| The stable conditions created a perfect stage for steep descents. Sellrain. (photo: 30.03.2019). |
