Full avalanche bulletin (to print) Page 1/4 Avalanche bulletin through Monday, 24 May 2021 23.5.2021, 16:57 High Alpine regions: Wind slabs are to be evaluated critically Edition: 23.5.2021, 17:00 / Next update: 24.5.2021, 17:00 Avalanche danger updated on 23.5.2021, 17:00 region A Level 3, considerable Wind slabs Avalanche prone locations Danger description As a consequence of a moderate to strong southwesterly wind, wind slabs will form especially in high Alpine regions. In addition the wind slabs of the last few days are capable of being triggered in some cases still. Avalanches can be released by people and reach medium size. Careful route selection is recommended. WSL Institute for Snow and Danger levels 1 low 2 moderate 3 consider. 4 high 5 very high Avalanche Research SLF www.slf.ch Full avalanche bulletin (to print) Page 2/4 Avalanche bulletin through Monday, 24 May 2021 23.5.2021, 16:57 region B Level 2, moderate Wind slabs Avalanche prone locations Danger description As a consequence of new snow and a moderate to strong southerly wind, easily released wind slabs will form in the course of the day especially adjacent to ridgelines and in pass areas as well as in high Alpine regions. These are to be evaluated with care and prudence. The number and size of avalanche prone locations will increase as the day progresses. In addition the somewhat older wind slabs should be taken into account. Persons can release avalanches, including medium-sized ones. Midday and afternoon: In high Alpine regions a considerable avalanche danger will prevail. Experience in the assessment of avalanche danger is important. Wet avalanches as day progresses As a consequence of the rain more frequent wet and gliding avalanches are to be expected as the day progresses, even medium-sized ones. This applies in all aspects below approximately 2400 m. Remarks The Avalanche Warning Service currently has only a small amount of information that has been collected in the field, so that the avalanche danger should be investigated especially thoroughly in the relevant locality. WSL Institute for Snow and Danger levels 1 low 2 moderate 3 consider. 4 high 5 very high Avalanche Research SLF www.slf.ch Full avalanche bulletin (to print) Page 3/4 Avalanche bulletin through Monday, 24 May 2021 23.5.2021, 16:57 region C Level 2, moderate Wind slabs Avalanche prone locations Danger description As a consequence of a moderate to strong southwesterly wind, wind slabs will form especially in high Alpine regions. In addition the wind slabs of the last few days are capable of being triggered in some cases still. Avalanches can in some places be released by people. The number and size of avalanche prone locations will increase with altitude. Caution is to be exercised especially in high Alpine regions. Careful route selection is recommended. Wet avalanches as day progresses In all aspects and below approximately 2400 m wet and gliding avalanches are possible as a consequence of the rain. From starting zones where no previous releases have taken place in particular on north and east facing slopes these can in isolated cases reach large size. Remarks The Avalanche Warning Service currently has only a small amount of information that has been collected in the field, so that the avalanche danger should be investigated especially thoroughly in the relevant locality. WSL Institute for Snow and Danger levels 1 low 2 moderate 3 consider. 4 high 5 very high Avalanche Research SLF www.slf.ch Full avalanche bulletin (to print) Page 4/4 Avalanche bulletin through Monday, 24 May 2021 23.5.2021, 16:57 Snowpack and weather updated on 23.5.2021, 17:00 Snowpack At heightened altitudes snow depths are above average for this juncture of the season. Particularly in the high alpine regions, conditions are wintery. Fresh fallen snow and snowdrifts from the last few days are still prone to triggering in some places on north-facing and east-facing slopes in high alpine regions more than anywhere else. As a consequence of daytime warming and the soon anticipated rainfall, small-to-medium wet-snow and gliding avalanches are possible below 2500 m in particular. Observed weather on Sunday, 23.05.2021 Skies during the nocturnal hours were heavily overcast for the most part. Precipitation was registered over widespread areas. The snowfall level in the northern regions descended from 2000 m down to 1500 m; in the southern regions from 2200 m down to 1800 m. In the early morning hours, skies cleared up starting in the west. Subsequently it became sunny, including in the eastern regions during the afternoon. Convective cloud build-up was registered. Fresh snow Between Saturday afternoon and Sunday morning, the following amounts of fresh snow were registered above 2200 m: · Main Alpine Ridge from Rheinwaldhorn as far as Bernina Pass, Silvretta: 15 to 30 cm; · in the other regions of Switzerland, in Trient, the Urner Alps as well as the other parts of Grisons south of the Rhine, as much as 20 cm. Temperature At midday at 2000 m, in the northern regions at 0 °C and in the southern regions at +4 °C. Wind Winds were blowing at moderate strength from westerly to southwesterly directions. Weather forecast through Monday, 24.05.2021 Nighttime skies on Sunday night will be predominantly overcast. In the northern regions, weather will be foehn-influenced. In the southern regions, precipitation is expected to set in, which subsequently will spread over the northern flank of the Alps during the course of the day. The snowfall level will lie between 1800 and 2200 m. Fresh snow The following amounts of fresh snow are anticipated above 2500 m by Monday afternoon: · Main Alpine Ridge from Monte Rosa as far as Bernina Pass and southwards therefrom: 10 to 25 cm; · in the other regions of Switzerland, generally less. Temperature At midday at 2000 m, at +2 °C. Wind Winds will be blowing at moderate to strong velocity from southerly to southwesterly directions. Outlook through Wednesday, 26.05.2021 On Monday night the precipitation will come to an end, including in the northern regions. On Tuesday and on Wednesday, skies will be variably cloudy. Some precipitation is possible in the form of showers. The danger of dry-snow avalanches demands attentiveness in the high alpine regions in particular. In addition, as a result of the daytime warming and solar radiation, wet-snow and gliding avalanches are possible. Current avalanche bulletin Feedback to avalanche warners Additional specialized federal departments Internet www.slf.ch (Avalanche released? Bulletin inaccurate?) MeteoSwiss (weather) / www.meteoswiss.ch App White Risk Questionnaire www.slf.ch FOEN (flood, forest fire) / www.bafu.admin.ch WSL Institute for Snow and (iPhone, Android) E-Mail [email protected] SED (Earthquakes) / www.seismo.ethz.ch Avalanche Research SLF Toll-free phone number 0800 800 187 www.slf.ch.