Mostly favorable conditions+beautiful weekend weather

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Summary

The outstanding weather forecast for the weekend permits us to look forward to making good use of the stable snowpack.

Influential weather factors of recent days were the cold fresh snow plus wind; fluctuating temperatures; heightened solar radiation; and intermittently strong settling of the snowpack. Depending on altitude and aspect, these factors became more, or less, relevant.

Review

The latest snowfall of Monday (25.03) and Tuesday was accompanied by plummeting temperatures (15 degrees lower) and regionally strong-velocity winds. Trigger-sensitive snowdrifts were generated which were predominantly small, easily recognized, deposited behind crests and in gullies and bowls.

A few centimeters of fresh snow fell on Monday, 25.3, and Tuesday, 26.3, amidst cold temperatures and regionally strong winds, as here on the Plattkopf in the Zillertal Alps.

We assign these snow masses only minor importance; moreover, they will soon recede to insignificance as temperatures rise. A latent, potential problem is the combination of crusts and faceted crystals, as described in the last blog To cause large-sized slab avalanches, a striking energy input is lacking.

Beneath melt-freeze crusts, weak layers often lurk which can serve as a fracture surface for slab avalanches. Here in Navistal, settling noises on south-facing slopes were heard and a slide remotely triggered. (photo: 24.03.2019).

Loose-snow avalanches can be either dry or wet; the latter type often occurs in combination with daytime warming. In the afternoon, the danger of being swept along by the snow also increases in steep, rocky terrain.

Loose-snow slides are a dominant picture every spring. At the moment, they are small. In photo from Härmelekopf, the negative factor is that these slides can cover huge distances; the positive factor is slabs cannot be triggered by them. (photo: 24.03.2019).

Gliding snow activity has receded and since the last major rainfall at mid-month only small areas have been set into motion. Like with other ongoing alpine dangers however, this does not mean they cannot become threats in each individual case.

Gliding snow release in Northern Massif, shot from a web cam on 24.03.2019.

The good conditions were taken advantage of during the last week, permitting ascents and descents on steep routes. The cold fresh snow was deposited atop a stable and irregular surface.

Gully on north-facing slopes in the Stubai Alps used for the ascent to 3000 m and the descent. (photo: 23.03.2019).

Man and dog get their reward when the fresh snow can be taken advantage of in good time, as here in Sellrain. (photo: 26.03.2019).

Since the problems referred to are limited spread, the map of the Avalanche Bulletin is full of green and yellow spaces. In other words, the weekend promises to be splendid. For tour planning, springtime conditions are the necessary axis of orientation, wintertime problems are withdrawing to the high alpine regions.

Snow situation

Thanks to snowfall at the beginning of the week, we are in positive zones as regards the 72-hour overall sum of fresh snow in northern Tirol (up to 30 cm in Lechtal and Karwendel), while the balance around the Main Alpine Ridge is negative.

Snow distribution of last precipitation. In distinction to the last blog, the fresh snow outdistanced the snowmelt.

In the valleys, spring has made its entry. It means that skis have to be carried on your back on ascents which begin at low altitudes. Don’t forget that it is still winter up at higher altitudes, complete with immense masses of snow.

Rapidly accumulating amounts of snow with ascending altitude, e.g. at the interface of Northern Massif and Innsbruck, bear witness to the highly distinct worlds of summer and winter.

Striking for this winter: the north/south distinction. In Ausserfern the snow depths are far above average, while the reserves from February in East Tirol have already evaporated.

Moisture

Model calculations demonstrate a very homogenous picture of snow temperature. These can only be interpreted as an indicator, since the calculation is coupled to air temperature.

The model of average snowpack temperature calculated by SNOWGRID reaches the freezing point over far-reaching areas.

Thorough moistening of the snowpack proceeds apace, naturally dependent on altitude and aspect. On sunny slopes the snowpack is isotherm up to high altitudes, especially on steep south-to-west facing slopes where the snow is shallow. On shady slopes and in general at high altitudes, there is still powder and loosely-bonded snow.

Stations where the snowpack surface temperature is measured indicate when the snowpack becomes thoroughly wet. The measurement is technically delicate, however, and subject to error when the snow on the surface becomes warm.

The surface temperature nears the maximum of 0 degrees for ever-longer periods, as here NW at over 2100 m; in other words, snowmelt. As a result of the cold front starting on the 25th, the snowpack surface was repeatedly cooled. However, it is starting to climb again and will reach 0° on the weekend.

Ordinarily, we refer to an isotherm snowpack (continuing constant temperature) when the temperature remains constantly at zero degrees. The snowpack then has no further buffer of cold and becomes throughly wet. Nocturnal outgoing longwave radiation can cool the snowpack, but only from the surface. This buffer (the zone of negative snow temperature between surface and ground) is currently a perfect illustration of the varied conditions.

Profile 1: W, 1900 m, 30°, Karwendel. The snowpack is isotherm and thoroughly weakened by moisture (©LWD Tirol). Profile 2: E, 1900 m, 25°, Verwall. The sun was sufficient to generate crusts, but insufficient to warm the whole snowpack. Nonetheless, there is no longer much leeway. (©Fun). Profile 3: N, 2700 m, 30°, Stubai Alps. Low air and snow temperatures in shady high alpine terrain. (© Lukas Ruetz). In red: the snow temperature.

Outlook for the weekend

According to ZAMG weather forecasts, residual clouds will disperse on Thursday, and the nighttime skies will often be clear. Following a chilly Friday morning with high fog in some areas, it will turn warmer during the daytime. On Saturday it will be springlike, with the zero-degree levels at about 2700 m. On Sunday, some light clouds are expected which could become dense and generate showers on Monday.

The nights will be clear, which means the snowpack will have strong outgoing radiation and freeze on the surface. This effect is countered by high air moisture (see illustration below) and the forecast inversion on Saturday, i.e. when the atmosphere releases more warmth to the earth’s surface).

Following a phase of low air moisture which enhances direct condensation of snow into water, since Monday (25.3) a phase of high air moisture has followed. This enhances snowmelt without condensation to the surface, on the one hand; and on the other, releases energy to the snowpack like clouds and amplifies the classic greenhouse effect. High air moisture effectively counters nocturnal outgoing radiation.

All in all, the daytime danger cycle of fluctuating dangers needs to be given greater attention at low altitudes and on sunny slopes. That means avoiding the breakable crusts. At higher altitudes, isolated snowdrift accumulations might be triggerable until greater settling has taken place. Caution is urged wherever these drifts are veiled by loosely-bonded slides. The snowpack layering is highly varied. Careful planning can increase the enjoyment.

Shortwave solar radiation is the greatest energy input into the snowpack, it can swiftly react to temperature limits. Shown here on the Schwarzhorn before the latest snowfall. (photo: 24.03.2019).

 (This blog was generated by our practicing apprentice Michael Reisecker.)

Heightened danger of wet loose-snow and isolated glide-snow + slab avalanches starting in late morning

Skies on Saturday night, 23.03, will again be star-studded and the snowpack will cool off accordingly. On steep, sunny slopes, a melt-freeze crust capable of bearing loads will form up to high altitudes in the early morning hours of Sunday. Beneath this crust the snowpack is wet or moist down to the ground at least up to altitudes of 2500 m where the slopes are steep. As a result of the intensive solar radiation typical of this juncture of the season and daytime warming, the melt-freeze crust will soften, more quickly on east-facing than on west-facing slopes. The snowpack thereby forfeits its firmness and can more easily be triggered.

Reviewing the last few days, it is apparent that the frequency of avalanches observed has increased day by day. Initially, avalanche activity was low; today, 23.03, we observed numerous releases, including four avalanches reported to headquarters in Tirol in which persons were involved. The victims sustained no injuries. (Mutmalspitze, Gurgler Massif; Arnplattenspitze and Handschuhspitze, Mieminger Massif; Malgrube, northern Stubai Alps). Currently the primary avalanche type is wet loose-snow avalanches. These can trigger naturally, in case the snowpack is sufficiently wet, or be triggered by external impulses, whether skiers, falling rocks or cornices.

Loose-snow avalanche above the Seegrube in the Northern Massif. A breaking cornice gave the decisive impulse for this wet loose-snow avalanche. No one was injured. (photo: 23.03.2019)

Naturally triggered loose-snow avalanche in Paznauntal  (photo: 23.03.2019)

Glide-snow avalanches are triggering only in isolated cases. Nevertheless, their nature is such that they remain utterly unpredictable.

An unusual sight: glide-snow avalanche over smooth rocks (Gletscherschliff); NE; 2400 m in the Zillertal Alps. (photo: 21.03.2019)

Slab avalanches are currently unusual, not the rule. Nonetheless, particularly on very steep, sunny slopes at high altitudes (above 2500 m), there are marked layers consisting of faceted snow crystals beneath melt-freeze crusts. If enough water seeps into such layers, which are generally encrusted or riddled with meltwater channels, the layer is correspondingly weakened. An avalanche triggering can therefore not be ruled out as of midday.

The arrow indicates a potential weak layer for slab avalanches in case the layer becomes thoroughly wet. (c) Lukas Ruetz, Stefan Herbke; profile from 21.03.2019

The generally small-sized snowdrift accumulations which were generated recently have no great significance. Only beneath the hardened wind crusts near the uppermost surface can we currently pinpoint weakened, faceted layers. They are of limited spread and generally not cohesive or area-wide. Such “nests” ordinarily become a problem only in extremely steep terrain when a patch breaks away and forces a skier to fall.

Beneath powder snow, a hardened wind crust; beneath that lurks a thin layer of faceted snow crystals. During a stability test, one part of the snow block remained in place. This fits into the overall picture of a predominantly favorable snowpack structure on shady slopes. North, 2790 m; 30 degrees  (photo: 21.03.2019)

The snowpack surface consists of...

...powder snow (photo: 21.03.2019)

....of a melt-freeze crust generally capable of bearing loads, sometimes breakable, on sunny slopes in early morning  (photo: 22.03.2019)

...later on, the snowpack becomes wet. With good planning, the reward is superb corn snow on steep, sunny slopes. (photo: 22.03.2019)

Other interesting information:

The snow is melting away...

The air-temperature and moisture sensors which were buried in snow until 20.03 are again in operation.

In the snowpack surface temperature (gray line in middle graph) the shrinking time windows are particularly evident.

Caution on glaciers. Everything from well-covered crevices to glacial surfaces which are bare area-wide can currently be found in Tirol. Wilder Freiger, central Stubai Alps (photo: 23.03.2019)

Favorable avalanche situation. Gorgeous weather for winter sports throughout Tirol

Current situation

Low avalanche danger currently prevails throughout Tirol. Brilliantly sunny-plus-no-wind weather has created unbeatable conditions for winter sports.

On shady slopes and in zones where solar radiation is flat, there is still powder snow. Breiter Grieskogel, southern Stubai Alps (photo: 20.03.2019).

The current avalanche situation permits steep descents with top conditions. Russkopf, Silvretta  (photo: 20.03.2019).

There are only few danger zones, as follows:

Snowdrift accumulations are prone to triggering only in isolated cases:

The wide-ranging snowdrift accumulations which were generated last week and at the beginning of this week by fresh snow and winds are no longer expected to trigger. They have bonded well with the old snow in all aspects. Fresh snowdrift accumulations are still trigger-sensitive in isolated cases, namely the drifts which were generated on Wednesday, 20.03. They are small, are found on steep, ridgeline shady slopes in high alpine regions. They require special caution, in particular as regards being forced to take a fall.

Slight daytime danger cycle:

Decisive for the current situation is the interplay of air temperature, solar radiation and humidity. Due to very dry air masses, the snowpack softens relatively slowly, in spite of intensive solar radiation and mild temperatures (zero-degree level over 3000 m). This is because the snowpack cools off enormously during the nighttime hours of star-studded nights and then forms a thick melt-freeze crust on the moist-to-wet snowpack surface. This first needs to soften, before the snowpack beneath it can moisten further. Incidentally, in the interim the melt-freeze crust on very steep sunny slopes is capable of bearing loads up to 2500 m. If backcountry tours are planned well, perfect corn-snow descents are assured.

There is currently little danger of moist or wet loose-snow avalanches. These are most likely to occur in extremely steep terrain during the afternoon, triggered by skiers.

Deposit of a wet-snow avalanche in the Stubai Alps. The corn-snow mirror glistens in the light of the sun. (photo: 17.03.2019).

Beware cornices:

A danger which should not be underestimated in this snow-heavy winter stems from cornices. They are extremely large in some places and can break and force one to take a fall. A fatal accident resulted from a cornice breaking on Tuesday, 19.03 on the Hohe Seeblaskogel in the Sellraintal. Due to warm temperatures and solar radiation, cornices can also break naturally to an increasing degree. As with glide cracks, risks can be minimized by circumventing the zones below cornices. In addition, extra caution is required in zones adjacent to ridgelines.

Huge cornices are currently found on many crests.  (photo: 17.03.2019).

When a cornice breaks, the zone behind the edge can also be endangered. (©Avalanche Canada).

On Hohe Seeblaskogel in the Stubai Alps, a fatal accident occurred on Tuesday, 19.03, as a result of a cornice breaking. In photo, the accident zone near the summit. (photo: 20.03.2019).

Isolated glide-snow avalanches are still a risk:

Glide-snow avalanches are being registered in extremely isolated cases, as here on Kitzbühler Horn. (photo: 20.03.2019).

Outlook

In the next few days, through Sunday 24.02, the weather is expected to remain sunny and warm. Thereafter a cold front will move in. It will bring some fresh snow and lower temperatures. According to ZAMG weather forecasts, the high-pressure system can then approach us anew. Temperatures are expected to climb again.

On Monday, 25.03, a cold front will reach us, bringing some fresh snow to the mountains. (©meteoblue).

Review

Last Friday, 15.03, and Saturday, 16.03, there was heavy snowfall, particularly in North Tirol and Hohe Tauern. As the snowfall level ascended in altitude on Friday night, numerous avalanches released naturally. They were mostly slab avalanches. In the rain-impacted lower-altitude regions, on the other hand, releases were mostly wet loose-snow avalanches. The slab avalanches triggered in the freshly fallen snow and in the snow which was transported by winds. The weak layer was loosely-bonded powder that fell on Wednesday night, 13.03, riddled with graupel in isolated cases.

Slab avalanche in Fieberbrunn ski area, probably released artificially after rain impact when the snowfall level ascended on Friday night, 15.03. 2000 m, SE.  (photo: 16.03.2019).

Naturally triggered slab avalanche on Gleirscher Rosskogel in the Stubai Alps. 2650 m, east. (photo: 16.03.2019).

Perfect example of a slab avalanche with a clearly visible wall separating fracture zone and plummet zone of the avalanche. Lampsenspitze, 2400 m, east.  (photo: 16.03.2019).

Slab avalanche, presumably triggered during the precipitation on Friday night, 15.03 or shortly thereafter. Granatspitzsattel, Venediger Massif, 2460 m, east. (photo: 17.03.2019).

As the snowfall level ascended on Friday night, 15.03, the snowpack became thoroughly wet up to 2000 m in many places.  (photo: 16.03.2019).

On the weekend of 16-17 March it was very warm (zero-degree level over 3000 m). Fresh snow and snowdrifts swiftly bonded with the old snow. Avalanche danger levels diminished accordingly. Subsequently, the major danger stemmed from freshly generated snowdrift accumulations.

As a cold front moved through on Monday, 18.03, there was snowfall down to the valley floor. Obertilliach, East Tirol. (photo: 18.03.2019).

As a result of moderate-strength winds, the loosely-bonded fresh snow of Monday, 18.03, was transported in some places. Small-sized, trigger-sensitive snowdrift accumulations were generated adjacent to ridgelines. Schnapfenspitze, Silvretta. (photo: 20.03.2019).

Heavily wind-impacted snowpack surface near ridgeline on the Arlberg.  (photo: 16.03.2019).

Heavy snowfall, gale-strength winds: dangerous avalanche situation!

Current situation & outlook

A powerful westerly/northwesterly airstream is currently thrusting a series of cold and warm fronts towards the Alps. By Saturday morning, 16.03, we can expect heavy precipitation, according to ZAMG weather forecasts. In the mountains, 50-100 cm of fresh snow is anticipated. Winds will be blowing at strong to storm strength, even reaching gale strength in some places tomorrow, Friday 15.03.

By Saturday morning (16.03) 60-100 cm of fresh snow is expected along the Vorarlberg border, 30-50 cm widespread in the remaining regions of North Tirol and Hohe Tauern.

Gale-strength winds are leading to wide-ranging snow transport of the fresh snow in some places.

 Deep-winter conditions on the Arlberg expressway after the perturbance arrived on Thursday afternoon. (photo: 14.03.2019).

The huge amounts of fresh snow, combined with strong winds, are ratcheting up avalanche danger levels. These will reach level 4, high, in the major areas of precipitation in the western regions of North Tirol. Elsewhere, considerable avalanche danger can be expected over widespread areas above 1800 m, and this rank lies at the uppermost border of the danger scale for level 3.

Potential weak layers for slab avalanches are currently found primarily in the uppermost section of the snowpack (excluding in southern East Tirol):

• The highly variable conditions and warmth, including solar radiation, of the last few weeks has led to the forming of numerous melt-freeze crusts, beneath which faceted snow crystals were generated. Snowpack analysis demonstrated no striking tendency to fracture propagation there, nevertheless fractures, at very least in the areas where snowfall has been heaviest, cannot be ruled out. We currently focus the threat on an altitude band between 2400 m and 2800 m in NE/ E aspacts. 

• The snow from Wednesday night, 13-14.03, cold, loosely-bonded fresh snow above 2200 m in wind-protected terrain, can potentially form a weak layer. 

• In addition, the current batch of fresh snow is also a potential weak layer for slab avalanches, since it was loosely deposited in wind-protected terrain and subsequently covered by snowdrifts.

During the variable weather of the last few weeks, numerous melt-freeze crusts were able to form, under which loose, faceted snow crystals are found in places.  (photo: 13.03.2019).

On Wednesday night, 13.03, there was snowfall, bringing a few centimeters of fresh snow over widespread areas at low temperatures. This fresh snow is a potential weak layer for slab avalanches.

Fresh snow and snowdrifts have been deposited atop a weak old-snowpack surface from region to region and can be triggered in all aspects above about 2200 m. The snowdrift accumulations are quite deep.

During the intensive periods of precipitation we expect numerous naturally triggered avalanches. Due to the sizeable amounts of fresh snow, the avalanches can be expected to reach large size. The higher temperatures resulting from the warm front on Friday, 15.03, will also bring about better bonding of the uppermost layers of the snowpack. Thereby, fractures can more easily be propagated. In addition, avalanche activity is expected to increase right at this juncture in time.

On Friday morning, 15.03, snowfall will presumably reach its climax. Simultaneously, temperatures will rise, and the snowfall level will ascend. We can then expect the culmination of naturally triggered avalanche activity.

An ascent of the snowfall level also means that increasing amounts of rain will penetrate the snowpack below 2000 m. Where this is heavy, the likelihood of loose-snow avalanches triggering on extremely steep slopes will increase. In addition, due to the rain impact and also due to the greater weight of the fresh snow on top of the snowpack, increasingly frequent gliding snow activity can also be expected, particularly on steep, grass-covered slopes below 2600 m, and especially below 2200 m.

In East Tirol there is a strong gradient from north to south with regard to the precipitation which is forecast. In the Hohe Tauern the snowfall will be heavy, bringing up to 70 cm. Further towards the south, the amount of fresh snow will swiftly decrease; south of the Drau, only a few centimeters are anticipated. Accordingly, avalanche danger levels are not expected to change significantly there. Danger is ranked as moderate in the Defereggen Alps, Schober Massif and Lienz Dolomites above 1800 m. The danger of generally small-sized snowdrift accumulations which can trigger primarily on shady, very steep, ridgeline slopes is also a threat.

Following the end of this period of precipitation on early Saturday morning, 16.03, weather conditions are expected to improve swiftly. The weekend promises lots of sunshine and warmth, according to ZAMG forecasts. The zero-degree level will ascend to 3000 m. The great amounts of fresh snow will rapidly become moist up to intermediate altitudes on sunny slopes. Numerous moist-snow and wet-snow avalanches can be expected on very steep slopes. Solar radiation and daytime warmth will also bring about better bonding of the snow masses, thereby leading to a short-term increase in the likelihood of slab avalanches triggering. Snowdrift accumulations will remain prone to triggering on shady slopes more than anywhere else.

On the coming weekend, it is important to ski defensively. The first day of good weather following a period of intensive snowfall and storm wind is particularly prone to accidents, as everyone knows.

Saturday, 16.03, and Sunday, 17.03, promise warm and dry weather. On Monday, 18.03, a cold front will arrive, bringing precipitation again. (©Meteoblue).

Review
Conditions were highly variable last week. Particularly Monday, 11.03, and Tuesday, 12.03, there was heavy snowfall (see  blog of 12.03.)). In the following days the weather was more pleasant, but strong westerly winds refused to slacken off. As a result, fresh snowdrift accumulations formed ever anew, particularly on shady slopes.

Variable weather with fresh snow, lots of wind and fluctuating temperatures. Falkaunsalpe weather station, N. Ötztal Alps.

As a result of the first solar radiation following the intensive snowfall of Monday night, 11.03, numerous loosely-bonded avalanches released in extremely steep, sunny, rocky terrain. Northern Massif.  (photo: 13.03.2019).

Fresh snowdrift accumulations were triggered as slab avalanches primarily on shady slopes. Stubai Glacier (12.03.2019).

During recent days, westerly winds were blowing predominantly at strong velocity in the Grieskogel Massif. (photo: 12.03.2019).

The fresh snow is clearly still powdery. This is visible in the snow cloud which the skier stirs up, and also in the snow plumes in the background. Gaiskogel, Stubai Alps  (photo: 13.03.2019).