Coming soon: a stable high-pressure weather front
According to ZAMG Weather Service forcasts, high-pressure conditions will increase ongoingly over the next few days. On Friday, 19.02, a cold front over Germany will send some clouds to Tirol. Starting on Saturday, 20.02, a stable high-pressure weather front will take over the reins. The zero-degree level is expected to lie at 3000 m. Light winds will prevail in the mountains.
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| The models all agree: in the coming week, no fresh snow in Tirol. |
Increasingly favorable avalanche situation
Superficial avalanche problems continually decreasing
These prospects will have a thoroughly favorable effect on the avalanche situation. Potential superficial avalanche problems we have observed over the last few weeks, e.g. snowdrifts, superficial old-snow problem, will recede into the background. Most of all, this is because over widespread areas only shallow slabs have formed during the last week atop potential weak layers. The energy now is reinforcing the bonding between slab and weak layer.
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| Snowdrift problem on 13.02.2021: the very loosely-packed fresh snow (fluffy powder) was transported by winds, generated very trigger-sensitive snowdrift masses for a short time. Grieskogel Massif. |
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| Since 7 February, potential weak layers have formed only on the uppermost surface. Warmth and solar radiation are now having positive effects on the situation. In the second crust in the above picture, a slightly yellowish hue is visible. This is from the recently deposited layer of sand from the Sahara. South, 2200 m, western Tux Alps. (photo: 16.02.2021) |
A very short excursion to avalanche danger of recent days from the perspective of avalanches being triggered by low additional loading. At first glance this fits both with danger level 3 (considerable) and danger level 2 (moderate). The reason: avalanche danger levels are published in accord with a number of different parameters.
- On the one hand, snowpack stability (and likelihood of avalanches triggering) is fed into this algorhythm: snowdrifts could be easily triggered.
- On the other, it is a matter of the distribution of avalanche prone locations. These occurred increasingly in ridgeline terrain and behind protruberances, in other words, were not widely distributed.
- In addition, both type of avalanche and size of avalanche play a huge role. We assumed small slab avalanches with a more shallow potential fracture depth.
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| Fresh drifted mass which triggered on a faceted weak layer (based on dp.4- cold on warm) in the Grieskogel Massif. (photo: 12.02.2021) |
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| Snow profile taken near the spots photographed above. Visible are the potential weak layers near a melt-freeze crust. Fractures were incomplete. |
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| A similar picture in the central Lechtal Alps. Weak layer with incomplete fracture, a slightly marked slab on top of that. South, 2230 m. |
Only a few other danger zones
What remains are avalanche prone locations on steep, smooth surfaces (especially on grass-covered slopes in East Tirol where snow was heaviest) where glide-snow avalanches can still trigger. This applies increasingly to steep sunny slopes. Glide-snow avalanches frequently ‘announce’ their triggering by glide cracks in the snowpack surface. For that reason, we advise: if possible, no stops near/below glide cracks.
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| Glide-snow avalanches on steep grass-covered slopes. Central East Tirol. (photo: 11.02.2021) |
In addition, a few avalanche prone locations where persistent, long-enduring weak layers at mid-level in the snowpack could be triggered. These last danger zones are likely to trigger only in spots where snow is shallow, in transitions from shallow to deep snow and then, in extremely steep terrain, by large additional loading. Most likely to trigger are W/NW to N to E/NE aspects between 2000 m and 2400 m. Furthermore we received reports from our South Tirolean colleagues of two avalanches 1-2 weeks ago in extremely steep S/E facing slopes along the Main Alpine Ridge at about 3000 m. Also there, they were isolated avalanche prone locations.
In addition, at high altitudes (above 2400 m) a small-spread snowdrift problem was noted, especially in shady terrain near ridges.
Worthy of note: this is only the very first daytime cycle of avalanche danger due to daytime warming and the springlike temperatures. Do not fail to get your daily information from the Avalanche Bulletin.
Snow quality is improving
Currently (18.02.2021) melt-freeze crusts dominate. Only in very steep sunny terrain, particularly at intermediate altitudes, is the snow transforming to firn. Firn snow, or more correctly, corn snow, will occur more frequently on sunny slopes at high altitudes during the coming days. Making a daytime tour time-plan is helpful in this regard, so that the snow has not softened by the time you begin your descent.
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| Firn snow at about 2000 m, south, Karwendel (photo: 18.02.2021) |
Short review of the last week
A brief intermezzo of very low temperatures, now history.
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| Initially (very) cold, now getting warmer... |
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| A similar picture in East Tirol... On 16 February the snowpack became moist. Uppermost layers thus bonded. The snowpack became more prone to triggering for a short time. |
On wind-protected spots, good powder...
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| On the weekend, often good powder (photo: 12.02.2021) |
