Numerous trigger-sensitive snowdrifts above timberline. We recommend enormous restraint in steep terrain.

Caution: 

Similar to 25.12.2018, the first day of the new year 01.01.2019 as "first fine-weather day" following a period of stormy snowfall is also an accident-prone day.

Snowfall and storm winds:

During the last two days in North Tirol and in northern East Tirol, there has been snowfall accompanied by formidable winds. The focal point of the snowfall was in the Lower Inn Valley and in northern East Tirol, where at high altitudes there was mostly 50 cm, but also as much as 100 cm of fresh snow registered.

Top windspeed velocities of 100 km/hr were not seldom in the mountains of Tirol in recent days. A great deal of snowfall was transported.

Trigger-sensitive snowpack:

Starting at the upper rim of the timberline the snowpack is prone to triggering. This has been corroborated by reports from skiers in these regions on New Year's Eve who observed both settling noises and glide cracks. In the Kitzbühel Alps on 31.12, skiers triggered an avalanche in shady terrain north of the 3S-Station near Jochberg. Nothing serious occurred. At 17:25 a report arrived at headquarters that near the Unterfaister Niederalm near Söll, an avalanche was released. We do not yet have any additional details

We also know that yesterday, 30.12, graupel showers moved over the land. Graupel, which is to say, powder snow blanketed by snowdrifts, currently comprise a rather wide-ranging and primal weak layer for slab avalanches. Secondarily, the faceted layers in the vicinity of crusts can also be triggered. Their typical altitude band: 2200 m to 2700 m, especially in the inneralpine regions and in the northern and central sectors of East Tirol. This includes all aspects. The altitude band in sunny terrain above about 2400 m is especially endangered.

To sum it up:
Whoever is currently in outlying terrain needs to have extensive avalanche knowledge and be defensively active, particularly above the timberline. Freshly generated snowdrift accumulations in steep terrain should be circumvented!

Outlook:

Wintery conditions are coming, also in southern East Tirol. For those engaged in winter sports, the conditions above the timberline are frequently treacherous. Additional information will be supplied in the course of the week.

Avalanche events of recent days

This blog entry is intended to provide a brief overview of the avalanche events of the last few days. For details, please consult here: most of these events occurred in the regions which are currently ranked with "considerable danger" (in addition in the Arlberg region).

In those regions in an altitude band between 2200 and 2700 m, there is an old snow problem in all aspects: in the middle section of the snowpack and near to the ground there are repeated layers of unbonded, faceted crystals, often in the vicinity of crusts. These loosely-packed crystals are the weak layer, on top of which is deposited a snowpack bearing formidable effects of wind from recent days. Snowdrifts, a weak layer and the additional weight of skiers and freeriders, and sometimes even the additional burden of solar radiation are the pre-requisites of the slab avalanches which were observed.

Avalanche accident Hohe Mut on 25.12. This was a very large slab avalanche. A snowboarder lost her life. A second person was able to escape to the orographic right. Fracture zone 2600 m, SW, parts 40°. Also visible is a second, remotely-triggered avalanche at the right upper edge of the photo. (photo: 26.12.2018)

Hohe Mut: view from the path of the avalanche towards Rotmoostal  (photo: 26.12.2018)

Hohe Mut: this snow profile was taken near the fracture of the avalanche. It reveals superficial snowdrifts and beneath that, a sequence of crusts and faceted crystals.  (photo: 26.12.2018)

Hohe Mut: place of burial (photo: 26.12.2018)

Some of the avalanches reported were remotely triggered:

Rastkogel: left of the avalanche, skiers escape the path. On the right, a slab avalanche triggers. (photo: 26.12.2018)

Avalanches on Zischgeles, presumably triggered by skiers and remotely triggered  (photo: 26.12.2018)

Avalanche Hoher Burgstall on 27.12: a backcountry skier was ascending when an avalanche triggered.  (photo: 27.12.2018)

Avalanche accident Weisser Knoten in the Grossglockner region. Four persons involved, no injuries.  (photo: 25.12.2018)

Glide-snow avalanches are a potential problem primarily where snowfall has been heavy, such as here in the Arlberg region.  (photo: 26.12.2018)

In southern East Tirol, in photo the Villgraten mountains, the snowdrifts are less deep than further north.  (photo: 25.12.2018)

In extremely steep terrain, a skier triggered this superficial avalanche today (27.12) below the Talsenhöhe in the Kitzbühel Alps, fresh snow, snowdrifts on top of a hardened rain crust. The person was apparently able to escape. (If the avalanche had been registered by calling tel. no. 140, we could have spared ourselves the expensive and arduous search party.)

Attentive observer on Pfuitjöchl. This avalanche is a moist unbonded-snow avalanche resulting from solar radiation and daytime warming.  (photo: 26.12.2018)

Outlook:

The old-snow problem will remain upright for a while. For that reason, we recommend all backcountry skiers and freeriders to avoid terrain which is very steep in the infamous zones.

Elsewhere, conditions are in general quite favourable. Only the snow quality leaves much to be desired.

As a consequence of the intensifying winds forecast by the ZAMG weather services for the weekend, however, increased attentiveness will be demanded by the fresh snow, particularly at higher altitudes.

Avalanches involving persons, one fatality. Cause: fresh snowdrifts and weak old snow.

At headquarters in Tirol today we were informed about 6 avalanches in which people were involved: Glorer Refuge and Marchkinkelle in East Tirol; Rettenbachferner Glacier, Serleskamm, Giggijoch and Hohe Mut in North Tirol. The last of these took human life. According to initial information of the Alpine Police, it was a large-scale release below the Hohe Mut in open ski terrain. This suggests a marked old-snow problem. Tomorrow, 26.12, we will investigate the incident together with the Alpine Police. For initial details, please click here:

Avalanche Hohe Mut on 25.12.2018. The ellipse shows the slope where the accident took place below the Hohe Mut in Obergurgl in open skiing terrain.

Strong-to-stormy wind influence in the mountains was striking on 25.12. In many places, snow plumes were observed in the vicinity of ridgelines. According to ZAMG weather headquarters, the winds are expected to slacken off.

The main danger in the coming days will stem from freshly generated snowdrifts which need to be assessed critically in steep terrain. Particular caution is essential at altitudes between about 2200 and 2700 m, since long-persistent weak layers are evident inside the snowpack near crusts there. Special attention is also called to the terrain adjacent to ridgelines, in gullies and bowls, where unbonded powder snow or fresh snow harbors deposited graupel which can serve as a (short-lived) weak layer for slab avalanches.

 Snow transport on Hohe Tor above Kals (photo: 25.12.2018)

Cornices on the Navis Kreuzjöchl in the Tux Alps  (photo: 25.12.2018)

Caution: beautiful weather after stormy period is particularly accident prone

The forecasts of the ZAMG weather service were correct. There has been much rainfall and snowfall in far reaching regions of Tirol. In addition, storm-strength NW winds were blowing in many regions at high altitude.

All in all over the last few days in the western regions of the land, there was at least 50 cm of fresh snow registered at high altitude, frequently 70 cm in the southwestern regions, and from place to place as much as 100 cm.

Disparites in overall snow depth. Some weather stations are at altitudes where there was persistent rainfall.

Precipitation distribution from 23.12 to 24.12, morning, for comparison

The rise in temperatures (rainfall up to 2000 to 2600 m) combined with precipitation and snowfall together with storm winds have weakened the snowpack. Up to intermediate altitudes, increasingly frequent wet unbonded-snow and glide-snow avalanches were reported. At high altitudes, naturally triggered avalanches released. These were large-sized,  triggered in all aspects, primarily in the western and southwestern regions of the land. The major activity was between yesterday 23.12 and today, 24.12, during the morning.


The weak layer was the graupel registered over wide-ranging areas yesterday on 23.12 . In addition, the faceted crystals near the crusts also played a role in the release of slab avalanches (sh. Schneeprofile).
The fact that some slab avalanches were also triggered on south-facing slopes at altitudes between 2300 and 2700 m points to the generation of danger pattern "cold on warm" since the beginning of December.

Upshot: particularly at altitudes between about 2200 and 2700 m in the middle part of the snowpack, or else near ground level, there are persistent weak layers, i.e. the beginning of an old-snow problem, which could prove triggerable over the coming few days. At higher altitudes, the covered (that is, drifted) powder snow could prove to be a weak layer, particularly adjacent to ridgelines on very steep, wind-protected slopes. Atop these weak layers, deep, brittle drifted masses have been deposited which increasingly in transitions from shallow to deep snow and, in general, wherever the snow is shallow, can be triggered.

Due to the quite widespread danger zones and the period of pleasant weather conditions which is being forecast over the Christmas holidays, we expect heightened likelihood of avalanche accidents. Today, on 24.12, we were informed at headquarters of one in Söll and one in the Axamer Lizum, the latter near to a ridgeline in very steep terrain on an east-facing slope at about 2200 m. Both proved relatively harmless, according to our current information. We hope these avalanche releases will inspire backcountry skiers to ski defensively on Christmas Day and in the days following. Don’t forget: experience shows that the first day of pleasant weather following a stormy period is particularly prone to accidents.

Increasing number of weak spots with rain and snow on the weekend - warm-thaw Christmas weather

Weather review

This last week has again been highly variable: sunshine, clouds, some precipitation. The extremely cold phase came to an end on 16.12, subsequent temperatures rose continually. Three phases of wind were observed: on 13.12 a strong southerly wind prevailed, on 16.12 winds shifted to westerly, on 19.12 winds again were southerly from region to region.

Weather station data from Plojen station / Planskopf in the Serfaus ski area

Danger situation

In the EUREGIO Tirol-South Tirol-Trentino, low and moderate avalanche danger levels prevailed over widespread areas. The main problem stemmed from freshly generated snowdrift accumulations (frequently adjacent to ridgelines) as well as gliding snow, also old snow from region to region.

Snow situation & snowpack

Tirol was draped in winter garb in many places. Nonetheless, the possibilities for backcountry tours continue to be very limited, at least at low and intermediate altitudes.

En route in the Stubai Alps. View into Senders Valley. Contact with stones cannot be ruled out... (photo: 18.12.2018)

Ski tracks near Jochberg in the Kitzbühel Alps. Grassy ground rises to meet the skiers. (photo: 15.12.2018)

We utilised the week sharpening our picture of snowpack layering in Tirol a further notch. All in all, it looks good. Least favourable by comparison is the layering on shady slopes starting at about 2300 m up to maximum 2800 m, where there are weak layers of faceted crystals inside the snowpack increasingly frequently, surrounded by melt-freeze crusts. (The crusts became thinner and softer during the most recent cold phase.) Weak layers are generally not cohesive over wide areas, for that reason tend to occur mostly near bowls or in the vicinity of small concavities in the terrain. Glide cracks and settling noises (whumpf!) were not observed during this last week.

Sequence of crusts and faceted crystals. Stubai Alps. NW, 2300 m (photo: 18.12.2018)

Weak layer of faceted crystals near ground-level on Predigberg in the Silvretta, N, 2100 m. (The old snowpack at this altitude is spatially limited, rarely cohesive or area-wide.) (photo: 18.12.2018) 

The structure of the snowpack surface is striking: during the most recent cold period, it became quite loose in wind-protected terrain. At least above the timberline there was frequent surface hoar evident, which then got covered in western regions of North Tirol. In isolated cases we received reports of Nigg Effect (surface hoar forming near ridgelines).

Surface hoar at the edge of the forested zone in the Kitzbüheler Alps (photo: 15.12.2018)

The wind impact referred to at the outset of the blog was also noticeable, particularly above the treeline. Increasingly frequently there are wind swirls evident, and thin melt-freeze crusts on sunny slopes in particular.

Wind ripples on the snowpack surface in the Silvretta (photo: 18.12.2018)

Avalanche activity

Last week, the report of a slab avalanche triggered by a skier in Fimbertal in the Silvretta arrived at headquarters in Tirol. Elsewhere it was rather quiet. However, activity involving glide-snow sluffs and glide-snow avalanches increased significantly on grassy slopes. The rise in temperatures reinforced this activity.

Photo left center, a freshly triggered glide-snow avalanche. Additional glide cracks and ‘wishbones’ bear witness to increased activity. Silvretta. (photo: 18.12.2018)

Glide-snow avalanches are a permanent threat in regions where there has been heavy snowfall. Hochfügen (photo: 13.12.2108) 

Outlook

Right on time for Christmas, warm-thaw weather announces its imminent arrival. It will soon become measurably milder. The precipitation will be rain at least up to intermediate altitudes. Winds will intensify and reach storm strength in some places.

The effect on the snowpack and avalanche danger levels is complex:
In regions exposed to rainfall, the snowpack surface will become moist, the loose layers of snow nearest to the surface will be destroyed. This is actually a positive development.

At higher altitudes, on the other hand, snowdrift accumulations will be generated afresh. Particularly where the drifts are deposited in very steep terrain which has been wind-protected to date, the proneness to triggering can be expected to increase. This trigger sensitivity will increase further as precipitation sets in and higher temperatures arrive.

In any case, the likelihood of glide-snow avalanches will increase significantly. Due to the higher temperatures and the rain, friction near ground level diminish, thereby raising the likelihood of releases.

Upshot: gliding snow on steep, grass-covered slopes and freshly generated snowdrift accumulations at high altitude will be the main danger.

Trigger sensitive snowpack in places

Recent avalanches showcase a trigger-sensitive snowpack, at least in certain regions. Two dangers threaten currently:

- Fresh snowdrifts

- Trigger-sensitive old snowpack regionally
 

Freshly generated snowdrifts are always easily triggered when unbonded fresh snow is transported at low temperatures. Both coordinates are currently fulfilled. It is very cold. There were strong-velocity winds in the foehn lanes on 13.12. That is the moment when even minimum additional loading is sufficient to trigger the snowdrifts in steep terrain. (Powder and decomposed snow crystals form a weak layer. The latter form will incrementally bond with the drifted masses in the coming few days.) 

Particularly along the Main Alpine Ridge, huge snow transport was observed today. Zillertal Alps.(photo: 13.02.2018)

Avalanche accident below the Spannagel descent in Hintertux Glacier ski area on 13.12.2018. The north-facing slope is very steep at 2500 m. Immediately prior to the avalanche, strong winds transported lots of snow onto this slope. Snowpack analysis carried out today, 13.12, showed that the fresh snowdrifts were prone to triggering. The primary weak layer was powder snow covered with fresh snow. (Secondarily, the layers of faceted snow crystals referred to above surely fractured from place to place.) The avalanche is about 100 m long and 200 m wide.

The police helicopter transports the dog guide down to the valley after the accident (photo: 13.12.2018)

Weak layers more deeply embedded inside the snowpack are currently a risk, particularly in the regions along the Main Alpine Ridge between about 2300 and 2900 m, especially on shady slopes. In the vicinity of (rain)crusts there are frequently loose, faceted snow crystals. These weak layers are not evident area-wide as a rule.

Small-scale, covered, naturally triggered slab avalanches in the Stubai Alps at about 2400 m (center of photo) indicate heightened trigger-sensitivity of the snowpack (photo: 12.12.2018)

Below the Pfaffenbichl, a slab was released while there were people on the descent. The fracture was located at 2300 m on an extremely steep north-facing slope. The fracture depth varied between 20 cm and 160 cm. Snowdrift accumulations from the weekend deposited atop faceted weak layers were triggered.

Avalanche accident from 12.12.2018 below the Pfaffenbichl (photo: 13.12.2018)

View from upper zone of the avalanche fracture towards avalanche deposit. Pfaffenbichl  (photo: 13.12.2018)

Snow profile of the upper avalanche can be viewed - as usual - here.

Also atop faceted snow crystals, this slab triggered in outlying terrain in the ski area Silvretta Skiarena in Ischgl when someone descended over it. Altitude: 2300 m, west, very steep (photo: 12.12.2018)

There is also positive news: 

Apart from the Main Alpine Ridge, older snowdrift accumulations have consolidated well in general. The main problem there currently: the predominantly small-sized, fresh snowdrift accumulations which are frequently found in shady terrain adjacent to ridgelines.

Predominantly good conditions on the Arlberg (photo: 13.12.2018)

Wherever snowfall has been heavy, we observe increasingly frequent glide-snow releases. These avalanches are usually small-sized, sometimes medium-sized.

Numerous glide-snow releases in Lechtal  (photo: 13.12.2018)

Glide cracks indicate potential threats. We recommend avoiding all spots below such cracks. (photo: 12.12.2018)

Outlook for the weekend: 

The strong winds today (13.12) are expected to taper off during the night tonight. Next to no further snowdrift accumulation is anticipated. However, the snowdrift accumulations which formed today are expected to remain prone to triggering for several days due to the low temperatures. The old snow problem which occurs regionally between about 2300 and 2900 m in the above-mentioned regions seems to be the major problem. Weather change is expected on Sunday, 16.12.

(What we need to keep an eye on: Danger Pattern 4 (cold on warm) particularly on sun-bathed slopes far removed from the regions where there has been the most snowfall.)

Restraint imperative after onset of winter

Winter has arrived in Tirol. Since Saturday, 8.12.2018, more than 100 cm of fresh snow has been registered at high altitudes.

Enormous amounts of fresh snow in far-reaching parts of Tirol

Review
On Friday 7.12 in far-reaching parts of Tirol, an intermediate high generated very pleasant weather conditions and mild temperatures. The zero-degree level during the day was at nearly 3000 m. The snow situation in widespread areas of Tirol was still rather meagre at that juncture. The snowpack, where there was one, was heavily wind-impacted and erratic.

Not much snow, and the snowpack prior to the snowfall was highly irregular, as here in the central Stubai Alps On the windblown ridges, the Sahara sand from the end of October comes to light (photo: 7.12.2018)

On Friday night and during the early morning hours of Saturday (8.12) a severe cold front moved in from the northwest, temperatures dropped abruptly (about 10° within the shortest imaginable time). Accompanied by storm-strength winds there was 5-10 cm of snowfall registered, the snowfall level at around 1000 m. Intensive graupel was also observed.

Lots of graupel has been observed over the last few days, Inn Valley (photo: 10.12.2018)

Snow profile in the Grieskogel group from 8.12.2018; NE, 2580 m, 26°. Beneath a thin layer of snowdrift, the graupel which fell on Friday night, 8.12 is recognizable. On a north-facing slope above 2400 m, weak, trigger-sensitive layers are evident in the old snowpack. (© Lukas Ruetz).

After a warm front brought some relief and only a touch of precipitation on 8.12, another cold front reached us on Saturday night in another storm-riddled NW airstream. The snowfall level descended down to the valley floor.

In North Tirol and the Hohe Tauern, 40-100 cm of fresh snow was registered at high altitudes, from place to place even more. Most was in typical NW barrier-cloud regions of the Silvretta and Samnaun groups over the Verwall group and Allgäu Alps into the Karwendel, as well as in the Wilden Kaiser. In the Deferegger Alps it snowed far less, about 10-20 cm; in the Lienz Dolomites, hardly at all.

Recent weather developments can be precisely observed in the automated measurements at the Pischgraben/Madleinkopf station in the western Verwall group. On Friday night (8.12) a cold front moves through, temperatures drop abruptly by more than 10° C and wind velocity soars. The weak warm front subsequently brings short relief before a new cold front makes temperatures plummet once again. Since the beginning of this period of precipitation, approximately 100 cm of fresh snow was registered at this measurement station. Winds blew constantly at strong to storm strength from the northwest.

In central Oetztal at 1400 m on Monday 10.12, about 35 cm of fresh snow was registered, about 50 cm at the treeline (photo: 10.12.2018).

Wintery landscape also in the Zillertal (photo: 10.12.2018).

As a consequence of the strong to storm-strength winds, wide-ranging snowdrift accumulations were generated above the treeline.

Wind as the architect of avalanches is here transporting the fresh snow, Tux Alps (photo: 08.12.2018)

Potential weak layers for slab avalanches can usually be found inside the fresh snow mass in the form of cold fresh snow or graupel. Naturally triggered avalanches reported during this period of precipitation presumably fractured in these weak layers.

Inside the old snowpack are weak layers on shady slopes between about 2400 and 2900 m. These consist of faceted snow crystals embedded between crusts. Stability tests have shown highly varied fracture tendencies, from high to low fracture propagation.

One also finds in high alpine, glaciated, shady terrain still expansively mettamorphosed snow crystals right on the glacial ice. This layer can probably trigger only in exceptional cases due to the compacted snow layer on it which goes back to the end of October.

Snow profile in the central Stubai Alps; N, 2615 m, 25°. On shady north-facing slopes a sequence of crusts and unbonded layers is often evident. Even though the snowpack prior to the recent precipitation was extremely irregular, slab avalanches fracturing in the old snowpack cannot be ruled out. (© LWD Tirol).

Outlook
As weather conditions improve from the west, the wind will also recede. Snowdrift accumulations are covered in some places, making them difficult to recognize. Since the prevailing low temperatures will persist, it will presumably take a few days for the drifted masses to bond well with the weakened layers inside the fresh snow masses. Thus, we advise a high degree of restraint in very steep terrain. Caution: the first period of beautiful weather following a period of storm-ridden snowfall is always prone to accidents.

Throughout Tirol, it was shiveringly cold on Tuesday morning (11.12). These low temperatures are expected to persist over the coming few days. They will hinder a rapid consolidation of the snowpack.

Otherwise needful of heed: on steep, grass-covered slopes the fresh snow can glide. Zones below glide cracks should be avoided whenever possible.

Also technical snow can be swept away as a glide-snow avalanche, as here in the Hochimst ski area. In the interim, this area is cloacked in deepest winter (photo: 05.12.2018).