---------------------------------------------------------------- WSL Institute for Snow and Avalanche Research SLF NATIONAL AVALANCHE BULLETIN NO. 124 for Saturday, 12 March 2011 issue date 11.3.2011, 18:30 hours ---------------------------------------------------------------- SLIGHTLY ESCALATING OF AVALANCHE DANGER AMIDST FOEHN WIND ---------------------------------------------------------------- CURRENT CONDITIONS On Friday it was sunny in the Swiss Alps. The midday temperatures at 2000 were between plus 1 and plus 3 degrees. On Thursday night, the wind was blowing at moderate to strong velocity, during the day on Friday at light to moderate strength from southwesterly directions. At high altitudes, particularly in the Valais and on the northern flank of the Alps, fresh, predominantly small sized snowdrift accumulations have formed. The snowpack in areas adjacent to ridge lines and in high alpine regions is often hard compacted and heavily influenced by winds. On wind protected, steep, north facing slopes, the snowpack is often intensely faceted and loosely packed. In some places, older snowdrift accumulations have been deposited on top of layers of coarse grained snow. Following nights with clear skies, steep, south facing slopes have crusts capable of bearing loads up to nearly 3000 m. SHORT-TERM DEVELOPMENT On Friday night in northern regions the skies will be partly clear, in southern regions it will be overcast. During the day on Saturday, it will continue to remain overcast in southern regions and above approximately 1400 m a few centimeters of snowfall is anticipated. In northern regions it will be partly sunny, accompanied by foehn winds. The midday temperatures at 2000 m will be minus 4 degrees in southern regions and plus 3 degrees in northern regions. The wind will be blowing from southerly directions. In the western regions, it will blow at moderate to strong velocity; in the southern and eastern regions, winds will be strong to storm-strength. Fresh, predominantly small sized snowdrift accumulations are expected to form. AVALANCHE DANGER FORECAST FOR SATURDAY Entire region of the Swiss Alps: Moderate avalanche danger (Level 2) As winds increase, the avalanche danger is expected to escalate over the course of the day, yet within the danger level "moderate". The avalanche prone locations are to be found primarily on wind loaded slopes of western to northern to southeastern exposition. In the Prealps, in the Bernese Oberland, in the central and eastern parts of the northern flank of the Alps, the hazardous zones are to be found above approximately 1800 m. In the Vaud Alps, in the Valais, Ticino and Grisons, the danger zones are found above approximately 2200 m. Freshly formed snowdrift accumulations can be easily triggered; the released snow masses are usually small sized, however. They should be evaluated with great care. In isolated cases, avalanches can also be triggered in the old snowpack. This is particularly the case on seldom frequented, steep, north facing slopes and applies to Upper Valais, the northern flank of the Alps and to northern and central Grisons more than anywhere else. With the exception of the southern flank of the Alps, moist sluffs and isolated wet snow avalanches can be expected in all regions over the course of the day, particularly on steep, sunny slopes below approximately 2500 m. TREND FOR SUNDAY AND MONDAY On Sunday in southern regions, 15 to 30 cm of snowfall is anticipated. On Monday, the snowfall will taper off. In northern regions on Sunday, it will be variably cloudy, yet will remain dry for the most part. On Monday it will be quite sunny. The foehn wind will be blowing at storm strength on Sunday, then slacken off on Monday. On Sunday, the avalanche danger is expected to escalate.