two days ago
Avalanche Bulletin
Monday, 06.02.2012, at 07:30
Caution urged towards small, easily triggered snowdrift accumulations above the treeline
Avalanche Danger
The avalanche danger level in Silvretta-Samnaun, Arlberg-Ausserfern and the western sector of the Northern Alps is moderate in general; elsewhere it depends on altitude and wind impact. Wherever strong winds have been blowing during the last few days, small but highly trigger sensitive snowdrift masses have accumulated, especially in ridgeline areas above the treeline in eastern to southern to northwestern aspects, but also in gullies and bowls. With a certain experience, these danger zones can be easily spotted. An additional peril remains the full depth snowslides which can slide down steep, grassy slopes from the ground. In spite of the icy temperatures, many such avalanches are being observed currently, which is why our recommendation to avoid all places below so-called glide cracks (which warn of imminent danger) remains in force. Such cracks appear with great frequency below about 2400 m on steep, sunny slopes.
Snow Layering
The snowpack surface is transforming, due to the extremely low temperatures. That means thin melt-freeze crusts at low and intermediate altitudes are increasingly dissolving. Subsequently, faceted snow crystals are forming in their place. In addition, surface hoar is being blanketed over by very dry, light snowfall. This kind of snowpack generally bonds quite poorly with snowdrift masses which are then deposited atop it. Thus, avalanches can be triggered with unusual ease by backcountry skiers and freeriders.
Alpine Weather Forecast (ZAMG-Weather Service Innsbruck)
Weather in general: a high pressure system which stretches from Siberia to central Europe is bringing icy cold, continental air masses to Tirol. Tomorrow, a low over southeastern Europe will supply us with moist air masses, the icy cold will temporarily recede, but return in the latter part of the week. Mountain weather today: it will be a very sunny, very cold day, protection against double-digit temperatures is imperative. Particularly in the Lower Inn Valley, visibility may be somewhat impaired by residual fog. Temperature at 2000 m: between minus 21 degrees in the eastern Lower Inn Valley and minus 13 degrees near the Ortler range; at 3000 m: minus 21 degrees. Light northeasterly winds, at higher altitudes, winds will reach moderate strength.
Short Term Development
As wind intensity increases, new snowdrift masses will accumulate
[Author: Patrick Nairz]
[Translated by Jeffrey McCabe]
yesterday
Avalanche Bulletin
Tuesday, 07.02.2012, at 07:30
Above the treeline, avalanche danger is considerable widespread
Avalanche Danger
The avalanche danger has risen significantly due to the influence of the wind, above the treeline the danger level is now considerable far and wide. Below that altitude, the danger level is often low, although it depends on the local wind influence over the last few days. The major peril stems from fresh, extremely trigger sensitive snowdrift accumulations which occur frequently in ridgeline areas in southeastern to southern to northwestern aspects and in steep gullies and bowls in all aspects. Caution: even hard, wind-compacted snowdrift can be easily disturbed. With experience in evaluating avalanche hazards, these danger zones can be easily recognized, provided the visibility is good. Further, caution is still required towards full depth snowslides which, in spite of the icy temperatures, can be released on steep, grassy slopes. Such slides can reach medium size, particularly in the regions of North Tirol where the snow is deepest.
Snow Layering
After being deprived for a longish period, southern East Tirol has finally received snowfall, about 20 cm. In remaining Tirol, there was only a small bit of new fallen snow. In addition, the wind has intensified throughout Tirol, which brings about the transport both of the fresh fallen snow and the cold, generally loose surface snow. Increasingly, snowdrift is accumulating which is highly prone to triggering. This is partly because surface hoar has formed atop the old snowpack and partly because the low temperatures have transformed the surface snow to faceted crystals. Snowpack analysis, together with reports from skiers and freeriders, confirm that the bonding of the snowdrift to the old snowpack is very poor.
Alpine Weather Forecast (ZAMG-Weather Service Innsbruck)
Weather in general: Tirol lies in the path of moist, cold air masses which will traverse the land from the east today. Tomorrow, Wednesday, it will turn drier and milder, especially in the mountains. Between Thursday and Friday, another bout of cold will strike. Mountain weather today: fog and clouds impede visibility. In addition, intermittent, light snowfall is anticipated. Windows of sunshine are most likely between the Lechtal Alps and the Silvretta, as well as on the glaciers west of the Brenner. The temperatures will be milder, but in high alpine regions the wind will intensify, thus making it seem colder. Temperature at 2000 m: between minus 22 and minus 15 degrees, rising further on Tuesday night; at 3000 m: between minus 20 and minus 12 degrees. Moderate easterly winds in high alpine regions; in East Tirol, the winds will be stronger.
Short Term Development
Freshly formed snowdrift accumulations are the primary hazard
[Author: Patrick Nairz]
[Translated by Jeffrey McCabe]
today
Avalanche Bulletin
Wednesday, 08.02.2012, at 07:30
Caution urged towards fresh, often trigger sensitive snowdrift masses
Avalanche Danger
The avalanche danger is contingent on altitude. Above the treeline, considerable danger generally prevails, below that altitude the danger level is often low and depends on wind influence. In the regions where snow is deepest, and where there are many steep, grassy slopes, the peril below the treeline is moderate, due to the increased hazards of full depth snowslides. The major danger currently stems from the freshly formed snowdrift accumulations, which are more prevalent than usual because of the ongoingly strong recent winds. Such snowdrift masses can now also be found below the treeline, particularly in the southern Ötztal and Stubai Alps; but more frequently, they appear in steep ridgeline areas in southern to western to northern aspects, as well as in steep gullies and bowls in all aspects, above the treeline. Caution: even hard, wind compacted snowdrift can be triggered with ease in steep terrain. In addition, the likelihood of triggering tends to increase during the afternoon on very steep, sunny slopes. The advantage is: snowdrift masses can be recognized with ease, provided one has experience in evaluating avalanche dangers. Continued caution is urged towards full depth avalanches on steep, grassy slopes, they can be released despite the low temperatures.
Snow Layering
In southern East Tirol, there has been an additional 10 cm of snowfall, in remaining Tirol there was none. The wind is the decisive factor in the present avalanche situation; the loose, cold snow is being increasingly transported. The bonding of fresh snowdrift with the old snowpack is thoroughly poor; the upper layer of the snowpack consists of surface hoar in some places, faceted, loose crystals in others. In places protected from recent winds, the snowpack is generally compact. Only in the regions along the Main Alpine Ridge on very steep, shady slopes above approximately 2500 m is there a fundament of depth hoar at ground level; this can be disturbed primarily where the snowpack is shallow through large additional loading.
Alpine Weather Forecast (ZAMG-Weather Service Innsbruck)
Weather in general: Tirol lies wedged between a high over northern Europe and a low over the Mediterranean, currently in the path of a mild and dry easterly air current. On Thursday, the next low will reach us from the northeast. Mountain weather today: above 1200 - 1500 m, sunshine will dominate, the clouds passing by will be above summit level. It will also be noticeably milder than in recent days, although quite windy to begin with. Temperature at 2000 m: minus 4 degrees; at 3000 m: minus 9 degrees. Brisk to strong southeasterly to easterly winds to start with, becoming weaker as the day goes on.
Short Term Development
The primary hazard is still from fresh, but easily discerned, snowdrift accumulations
[Author: Patrick Nairz]
[Translated by Jeffrey McCabe]
current pattern(s)
current danger pattern(s)
Experience has shown that even over the course of highly varied winters, nearly identical potential-avalanche scenarios repeatedly arise as recurring danger patterns and are responsible for the greater part of avalanche accidents. An analysis of these patterns was published in the practical handbook _Avalanche - Recognizing the 10 Decisive Danger Patterns_ by Rudi Mair and Patrick Nairz in November 2010.
danger pattern (gm) 5 - snowfall after a long period of cold
A classic scenario in avalanche situations: following a long period of low temperatures, it begins to snow. In addition, a strong wind is blowing, which transports the freshly fallen snow. Within the shortest imaginable time, an extremely treacherous situation for skiers and boarders arises. Yet this is equally true when, following a long period of low temperatures, _merely" a strong wind blows, without any snowfall. The underlying problem: on wind protected slopes, fresh snowdrift accumulates which usually is deposited atop an old snowpack consisting of depth hoar. The old snowpack and new snowdrift are very poorly bonded to each other. The snowpack then just waits to be triggered by a new disturbance.
danger pattern (gm) 8 - surface hoar blanketed with snow
Surface hoar, aesthetically, numbers among the most beautiful types of snow. It is not a potential danger in itself. However, when it is covered over by new, bonded layers of snow it becomes a peril and is thus considered, with reason, to be one of the most critical weaknesses in snow analysis and avalanche science.
danger pattern (gm) 2 - sliding snow
Snowslides are usually unleashed down towards the valley across steep, smooth slopes. Before they are released glide cracks form, i.e. easily visible fissures in the snowpack, often several meters deep. Quite opposed to an age-old belief which is still difficult to dispel, such glide cracks are now known to be not favourable signs, but on the contrary, thoroughly unfavourable harbingers of full depth snowslides. A glide crack points to the possibility of a full depth snowslide, though gives no indication about whether a snow mass will actually be triggered as a full depth snowslide and, if so, when. Full depth snowslides are among the most difficult types of avalanche to predict, in terms of their time of triggering, because they can be released literally at any time of day or night even in generally stable snow conditions, on the coldest day of winter or the warmest. Furthermore, full depth snowslides are not unleashed by additional loading.
