Springtime conditions on the increase

After brief delicate situation for winter sports enthusiasts, quite favourable conditions

Last week was marked by superb powder and favourable conditions as well as a delicate avalanche situation for winter sports enthusiasts. This was on Tuesday, 10-11.03 when a warm front passed over Tirol and numerous naturally triggered avalanches released. These were also observed on 11.03 in the morning hours when diffuse radiation impact weakened the snowpack. The following dry air masses and star-studded skies on Wednesday night (11-12.03) improved the situation, and Thursday was hit by classic springtime conditions with a daytime danger cycle.

Striking: sunny 08.03; warm front on 10.03, initial rise of snow depths, then massive settling due to rain and sun; wet snowpack with outgoing radiation on 11-12.03; a melt-freeze crust forms which can carry loads in places. Snowpack softens as a result.

Then until 14.03 follow two weak cold fronts. Avalanche science points to potential glide-snow avalanches on steep grass-covered slopes and loose-snow avalanches. In very isolated cases there are recently formed snowdrift masses which can be triggered, particularly on shady slopes above about 2800 m. In addition, the fronts referred to also form small, fresh snowdrift masses. Caution is required most at high altitudes in ridgeline terrain in the western regions of North Tirol, i.e. where precipitation was heaviest.

Impressions from this last week

A dream day, full of backcountry skiers throughout Tirol: 08.03.2020. Defereggental. 

Powder in East and North Tirol. Here, descent from Kleinen Kaserer in the Tux Alps. (photo: 08.03.2020)

Very steep terrain was also used and skied. Rosskogel, Stubai Alps. (photo: 08.03.2020)

Finest very light fresh snow in the Tux Alps. An interesting thing was observed: the skins curled up while the snowpack was still dry. That happens only when the snow is extremely loose, the air very dry and radiation already quite intensive. As a result, due to very high temperature disparities, a weak layer was able to form in the uppermost layers of the snowpack (“radiation recrystallisation”). The prerequisite for this was lacking, due to the ongoing weather development.

Avalanche releases were few, in view of the many winter sports enthusiasts who were in outlying terrain. Avalanches were generally small-sized. There was also the risk of being swept along. This happened to one climber in the Wilder Kaiser, who was injured.

Avalanche release Mädelegabel in Ausserfern. (Surface hoar seen here as weak layer, for a short time). (photo: 08.03.2020)

Avalanche release Goinger Törl (photo 08.03.2020). Somewhat unclear is the weak layer, possibly a local, briefly relevant dp.4 (cold on warm) adjacent to a ridgeline, shady slope.

Near the upper avalanche. Shallow slab near a ridgeline on Kleinen Törl. (photo: 08.03.2020)

Warm front on 10-11.03

Please refer to the Blog on 10.03.
The warm fron led to a marked rise in avalanche danger and to high naturally triggered avalanches because the front initially still bore snowfall which transformed to rainfall up to about 2400 m. Thus, a perfect weak layer in the form of cold powder and decomposed crystals existed. The slab formed through the warmth and also through the wind at high altitudes.

Precipitation on 09.03, then a warm front on 10.03, snow changing to rain

Rainfall levels in Tirol at the end of the warm front

In steep terrain, shallow fractures could be provoked rather rapidly during the precipitation. This proves the high proneness to triggering. (photo: 10.03.2020)

In western regions the precipitation was more intensive than expected. The avalanche bulletin was updated for that reason and for 11.03 high danger published for a brief time. High danger (“Ski Tour High”) was also justified for the neighbouring regions in retrospect, where there was more snowfall. Further to the east where there was less precipitation the avalanches were correspondingly smaller. In general, these were superficial slab avalanches and loose-snow avalanches as forecast.

Avalanche releases in the Silvretta. (photo: 11.03.2020)

...some of which reached ascent paths to refuges. (photo: 11.03.2020)

Avalanche releases in Sellraintal. (photo: 11.03.2020)

Avalanche deposit in Zillertal. (photo: 11.03.2020)

Small loose-snow avalanche in Tux Alps. (photo: 11.03.2020)

Successful artificial triggerings. Ötztal. (photo: 11.03.2020)

Artificially triggered avalanche in Pitztal. (photo: 11.03.2020)

Central East Tirol and southern East Tirol were hardly touched by the warm front.

A freerider was lucky in the Wasserkar (Ötztal): swept along by a slab avalanches and buried. After 10 minutes he was dug out of the snow masses uninjured . (photo: 11.03.2020)

Rapid stabilisation as a result of improved weather

When loose powder forms a weak layer, it provides a great advantage over persistent weak layers, since the powder swiftly bonds with the snowdrifts deposited on top of it. This is even more the case when solar radiation is intense and/or temperatures are high. Currently, both are the case. For that reason, the snowpack has stabilised very quickly. Avalanche danger receded swiftly, but rose again in the daytime today on 12.03 due to solar radiation and relatively high temperatures. Water which seeped into the snowpack weakened it superficially.

Impressive shot of water collection zones via photo-working by Lukas Ruetz. (photo: 11.03.2020)

A typical profile in sunny steep terrain currently. Sequence of crusts. Isotherm snowpack. No fracture propagation.

Spring is coming - heed daytime avalanche danger cycle

According to ZAMG Weather Service, following the short weak cold front, a persistent warm period of fine weather will follow as of Sunday 15.03. For winter sports enthusiasts that means: whoever starts out early is doubly rewarded. Avalanche danger conditions are more favourable than later in the day. And with good route planning there is wonderful firn snow to be enjoyed.

Avalanche dangers are expected to be quite recognizable. Attentiveness is required towards the quite large cornices at high altitudes.

Brief delicate situation in backcountry. Be careful of naturally-triggered avalanches!

The warm front forecast by ZAMG Weather Service arrived today, 10 March, and brought widespread snowfall to Tirol, rainfall at low and intermediate altitudes.

24 hrs of precipitation (as of 10.03, 19:00) which, according to ZAMG Weather Service will terminate at about midnight.

Snowfall at high altitude, increasing rainfall at low and intermediate altitudes due to rising temperatures. Strong-to-stormy winds at high altitudes. Hot spot: esp. western and northern regions of North Tirol.

This has increased avalanche danger significantly as a result, to considerable in the regions where snowfall was heaviest. We observe already this evening at high altitudes increasingly frequent naturally triggered avalanche activity. Avalanches (mostly small-sized) can be triggered by minimum additional loading. A very loose layer of fresh snow can serve as a weak layer. The slab which is necessary for slab avalanches is forming on the surface due to rising temperatures, and tomorrow due to increased solar radiation.

First small avalanches during heavy snowfall and rising temperatures. Silvretta. (photo: 10.03.2020)

Winter sports enthusiasts triggered this slab today (10.03) with a fracture depth of 10 cm. Such a minor fracture depth indicates a very reactive weak layer (loose powder and decomposed snow). Silvretta. (photo: 10.03.2020)

Tomorrow (11.03) we can expect more frequent superficial slab avalanches as a result of the solar radiation, especially on sunny slopes where residual cloud persists, but also on shady slopes due to diffuse radiation. This will occur increasingly in regions where precipitation was heaviest. In addition, numerous loose-snow avalanches can be expected in extremely steep terrain and isolated glide-snow avalanches on grassy slopes.

In short: whoever is in outlying terrain tomorrow needs very good knowledge of the terrain and an ability to assess the risks on-site.

In the regions where precipiation was less, the situation is better. But there, a daytime rise in avalanche danger requires caution due to higher daytime temperatures.

Mostly favorable conditions. Be careful of fresh high-altitude drifts and loose-snow avalanches.

Predominantly favorable conditions

Avalanche danger in Tirol is moderate above 2200 m, elsewhere danger is low. Highest caution is necessary towards fresh snowdrift masses, especially trigger-sensitive on very steep shady and ridgeline slopes at high altitudes. In addition, the fresh snow reacts very swiftly to solar radiation and diffuse light in this season, meaning that increasingly frequent loose-snow avalanches can be expected on extremely steep slopes.

With good planning it was possible to enjoy powder last week. Avalanche prone locations were not large and easily recognized. (photo: 28.02.2020)

Danger level map for 06.03.2020

Weather review

Variable conditions
This last week was highly variable: warm and cold fronts brought continual precipitation (snowfall above 1000 m). In between there was sunshine. Strong to stormy winds were always present.

Once again: variable weather, e.g. at Axamer Lizum. Particularly striking: brief high windspeeds on 27.02 and 28.02. 

Wind impact and snow transport on Hintertux Glacier (photo: 29.02.2020)

Weather review in detail (by Marco Knoflach)

Last Saturday (29.02.2020) the second warmest February in history came to an end with a westerly foehn air current, bringing mild air masses our way before on Saturday night (01.03.2020) a cold front made temperatures drop. The widespread low over northern and central Europe brought quite wet and late-wintery cold air masses to the Alps. Following a brief intermediate high on Wednesday (04.03.2020) the next perturbance will pass through today (05.03.2020).


Snowpack

Overall snow depths at high altitudes correspond to average depths for this juncture of the season.

Snow depths are below average at low and intermediate altitudes, average at higher altitudes.

Snow depths in Kühtai. The dark line shows the current depth, near to the average level.

Typical snow distribution in Tirol. View from Mieming mountains towards northern Stubai Alps. (photo: 01.03.2020)

Fresh snow was distributed in repeated bouts during the week.

The fresh snow was a positive contribution, most of which was deposited in East Tirol

Weather station Thurntaler near Sillian in southern East Tirol. Easily recognized: increased fresh snow on 01-03.03.

Innergeschlöss (photo: 03.03.2020)

Problem zones are most likely inside the fresh snow near the surface.

The snow profiles obtained over the last week in Tirol were generally stable. Only surface-near layers were triggerable for a short time.

Glide cracks when treading the snowpack and superficial drifts gliding away. Schober Group. (photo: 04.03.2020)

Massive graupel layers were conspicuous.

Grains of graupel inside the fresh snow. Potential weak layer only where they were several centimetres thick. East Tirolean Main Alpine Ridge. (Graupel was also observed in the Tux Alps.) (photo: 04.03.2020)

Indicative for the current situation: no fractures during stability tests. Graupel layers near the surface.

Snowpack is moist up to intermediate altitudes, yet stable. Jöchelspitze, Ausserfern (photo: 01.03.2020)

Twigs and pine cones inside the snowpack demonstrate massive wind impact. Tux Alps. (photo: 03.03.2020)

Activating persistent weak layers (old snow problem) is known and not known. Conceivable on shady very steep slopes near the treeline in southern East Tirol.

Naturally triggered avalanche in Obertilliach. The avalanche appears to be a near-surface snowdrift problem. In very isolated cases, this region has fractures of expansively metamorphosed (faceted) layers which recently formed below the melt-freeze crust in places where snow was shallow. Avalanche releases were small-to-medium. (photo: 05.03.2020)

Change from dry to moist snowpack surface

Appropriate to this juncture of the season, the snowpack surface currently becomes moist quite rapidly from diffuse solar radiation.

Recognizable in the rocks: the flowing melt-water. Mieming Massif. (photo: 01.03.2020)

Reserved for the fittest backcountry skiers: accumulating moistened surface snow, beneath that dry snow. Tannheimer Tal. (photo: 01.03.2020)

En route in outlying terrain on the way to Pforzheimer Refuge. The sun, which is visible, is causing striking warmth inside the snowpack which enhances the stabilization of freshly-generated snowdrift masses. (photo: 05.03.2020)

Avalanches during the last week

Only a few avalanches involving persons occurred to our knowledge during the last week. With all avalanches, fresh snowdrifts were released on very steep to extremely steep slopes.

Avalanche Wanglspitze. Two persons were able to escape the avalanche near the upper fracture zone of the release. (photo: 28.02.2020)

Close-up of the photo above. Wanglspitze  (photo: 28.02.2020)

Avalanche Hinteres Rendl (photo: 28.02.2020)

A quite typical slide. Stubai Glacier (photo: 01.03.2020)

Artificial triggerings with explosives were generally without much success last week.

Visible is the crater caused by the explosion. Minor-to-medium success. (photo: 01.03.2020)

What’s next?

The weather will remain variable in coming days. Stable conditions are not in view, according to ZAMG Weather Service. Seen from today’s perspective, Sunday will be dry (08.03.2020).

During the next few days, powder snow can always be enjoyed, like here on the Main Tauern Ridge on 01.03.2020.

The main danger will continue to stem from fresh snowdrifts at high altitudes, and in particular on very steep ridgeline slopes. Also, as was the case in the last few days, we have to expect loose-snow avalanches.

Loose-snow avalanches following snowfall. Northern Massif. (photo: 28.02.2020)

Needs to be critically assessed: ridgeline terrain during and immediately after snowfall-plus-wind.