---------------------------------------------------------------- WSL Institute for Snow and Avalanche Research SLF NATIONAL AVALANCHE BULLETIN NO. 132 for Sunday, 20 March 2011 issue date 19.3.2011, 18:30 hours ---------------------------------------------------------------- AVALANCHE DANGER IS CONSIDERABLE FAR AND WIDE ---------------------------------------------------------------- CURRENT CONDITIONS On Saturday in Ticino it was predominantly sunny. In the remaining regions it was heavily overcast for the most part, accompanied by snowfall on the northern flank of the Alps in particular. Since Friday night on the northern flank of the Alps there has been 10 to 20 cm of snowfall; in the Valais, in northern and central Grisons, 5 to 10 cm of new fallen snow. All in all, between Wednesday and Saturday above approximately 2200 m on the northern flank of the Alps from the eastern Bernese Alps to Liechtenstein, in northern Grisons and in the Engadine, there has been 25 to 40 cm of fresh fallen snow, from place to place as much as 50 cm, elsewhere 10 to 25 cm of snowfall. The midday temperatures at 2000 m on Saturday were minus 3 degrees in northern regions and plus 1 degree in southern regions. The wind was blowing at light to moderate velocity from northwesterly directions. The old snowpack is thoroughly wet in all expositions below about 2200 m. The new fallen snow and the snowdrift from the last few days, particularly on west to north to east facing slopes, has been deposited on top of an old snowpack which is weak and prone to triggering from region to region. SHORT-TERM DEVELOPMENT On Saturday night, a small amount of additional snowfall is anticipated. During the day on Sunday, it will be sunny in most regions. The midday temperatures at 2000 m will be minus 1 degree in western and southern regions, minus 3 degrees in northern regions. In northern regions, the bise wind will be blowing at moderate to strong velocity, especially during the night, elsewhere the wind will be moderate, from northeasterly directions. Particularly in the regions with new fallen snow, snowdrift accumulations are expected to form afresh. AVALANCHE DANGER FORECAST FOR SUNDAY Entire region of the Swiss Alps not including the regions of central Ticino, Sotto Ceneri, southern Val Calanca, southern Val Moesa: Considerable avalanche danger (Level 3) On the northern flank of the Alps from the eastern Bernese Oberland to Liechtenstein not including the Gotthard region, the avalanche prone locations are to be found on steep slopes in all expositions above approximately 1800 m. On the Main Alpine Ridge from the Matterhorn to Oberalp Pass, in northern Ticino and in the indicated regions of Grisons, the avalanche prone locations are to be found primarily on steep slopes of southwestern to northern to southeastern exposition, and in areas adjacent to ridge lines and pass areas in all expositions, above approximately 2200 m. The major peril stems from the new fallen snow from the last few days, together with the freshly formed snowdrift accumulations. Avalanches which attain medium size are possible. In the remaining western part of the northern flank of the Alps, in the Lower Valais and in the Upper Valais not including the Main Alpine Ridge, the avalanche prone locations are to be found primarily on steep slopes of western to northern to northeastern exposition, as well as in areas adjacent to ridge lines and pass areas in all expositions, above approximately 2200 m. Particularly on north facing slopes, it is possible to trigger avalanches in the old snowpack. In addition, freshly formed, usually small sized snowdrift accumulations should be avoided whenever possible. For backcountry skiing and freeriding tours in all regions of the Swiss Alps, experience in the evaluation of avalanche hazards is imperative. Due to the daytime warming cycle, the likelihood of dry avalanches being triggered will escalate somewhat over the course of the day. Central Ticino; Sotto Ceneri; southern Val Calanca; southern Val Moesa: Moderate avalanche danger (Level 2) The avalanche prone locations are to be found on steep slopes in all expositions above approximately 2000 m. A prudent route selection, and maintaining distances, are important. In all regions, the danger of wet snow avalanches is expected to increase over the course of the day. Below about 2200 m, on south facing slopes below about 2800 m, naturally triggered wet avalanches are possible. Backcountry skiers and freeriders in outlying terrain away from secured ski runs can trigger avalanches in the thoroughly wet old snowpack particularly at altitudes between 1800 and 2200 m. This is especially the case on north facing slopes. TREND FOR MONDAY AND TUESDAY On both days, it is expected to be sunny. A moderate northeasterly wind will prevail, the temperatures are not expected to change significantly. The danger of dry avalanches will subside. The danger of wet snow avalanches will heighten during the course of each day.