1e lawinebericht van winter 12-13

[b]National avalanche bulletin[/b]

_valid through Monday, 03 September 2012

issue date 30.8.2012, 18:30 hours_

Snowfall to below 2000 m, increase in avalanche danger particularly in high alpine regions

[b]Current conditions[/b]

Following a month of generally sunny and hot weather in August, there was snow remaining merely on the glaciers in high alpine regions. Even there, snow was mainly found only on north facing slopes above approximately 3500 m. Thus, the anticipated snowfall is currently falling for the most part on bare ground or on sheer ice.

[b]Development[/b]

During the evening of Thursday, 30 August, a cold front has been sweeping across Switzerland. It brings intense precipitation with it, particularly along the northern flank of the Alps, which will continue until Saturday. By the morning of Friday, 31 August, the snowfall level will drop from over 3000 m down to 2000 m; then on Friday night drop further to 1600 m.

By midday on Saturday, 1 September, the following amounts of new fallen snow are expected above 3000 m: northern flank of the Alps, 60 to 100 cm; Valais, Ticino and Grisons, 30 to 60 cm.

At 2000 m on the northern flank of the Alps, 10 to 20 cm of fresh fallen snow is anticipated; in the Valais, in Ticino and in Grisons, as much as 10 cm of snowfall. The wind will generally remain weak, on Friday night temporarily intensify to moderate to strong velocity from northerly to northeasterly directions. As a result of the winds, snowdrift accumulations are expected to form in high alpine regions in particular.The precipitation will taper off on Sunday, 2 September, but skies will remain predominantly overcast. On Monday, 3 September, it is expected to be dry. Temperatures are expected to rise.

[b]Avalanche danger[/b]

The danger of dry avalanches will be heightened above 2500 to 3000 m in particular. Avalanches can be triggered by a single person. Naturally triggered avalanches which attain medium size are possible especially on the northern flank of the Alps. The conditions for high alpine mountaineering is unfavourable. Below 2500 to 3000 m, naturally triggered wet snowslides can be expected on smooth, grass-covered slopes and rock slabs. The perils of being swept along and falling should be taken into consideration. In particular, sluffs on roadside embankments can endanger high altitude, exposed transportation routes in isolated cases. On Sunday, 2 September, and Monday, 3 September, the hazards of dry avalanches will gradually subside. The peril of wet snowslides will remain upright, due to rising temperatures and local rainfall.

[b]Outlook[/b]

The development of weather conditions as of Tuesday, 4 September, is still uncertain. The danger of avalanches in high alpine regions should continue to be given all due consideration. The next avalanche bulletin will be published upon the next heavy snowfall. Avalanche hazards continue to require all due attentiveness, especially in the case of new fallen snow.

source: SLF