Avalanche danger will increase with heavy snowfall and wind through the day Friday.
New snow accompanied by moderate wind will build reactive storm slabs over the day Friday. At treeline and below, a crust beneath the storm snow provides an excellent sliding surface for avalanches.
Thursday night: Snow, accumulating 20-30 cm overnight. Light variable winds. Alpine low temperatures around -8. Freezing level valley bottom.
Friday: Continuing snowfall, 30-40 cm through the day with another 10-20 cm overnight. Moderate to strong southwest winds. Alpine high temperatures around -5. Freezing levels rising late in the day, as high as 1500 m near the coast, but should stay below 1000 m at Shames.
Saturday: Mostly cloudy with continuing flurries bringing 5-15 cm of new snow over the day and continuing overnight. Moderate southwest winds. Alpine high temperatures around -4.
Sunday: Clearing skies with isolated flurries bringing a trace of new snow. Moderate northwest winds. Alpine high temperatures around -6.
A natural windslab avalanche cycle up to size 2.5 occurred on Wednesday on northeast to southeast aspects in response to intense wind transport in the alpine and treeline. As more snow falls ontop of this windslab under calmer wind conditions, triggering of storm slabs could continue to be focused on lee features, but involve even larger volumes of snow. At treeline and below, a crust beneath the wind/storm slab provides an excellent sliding surface for avalanches.
Heavy snowfall overnight and throughout the day will bring new snow totals to 50-70 cm by Friday evening. The new snow fell on a temperature crust up to treeline and extensive windslab at alpine and treeline elevations. The underlying snowpack is overall quite well consolidated, with an average depth of around 2 m. Two layers of surface hoar are now buried 80-150 cm deep but with a lack of recent associated avalanche activity, appear to be trending towards dormancy.
