Fresh wind slabs will form with moderate southwest wind in alpine lee features and below ridge crests. Be alert to conditions that change with elevation and wind exposure.
Moderate southwest wind will build fresh slabs. Be especially mindful around steep and convex openings in the trees and ridge features in the alpine.
A deeply buried weak layer has produced a number of large and surprising avalanches in the past week and a half. This problem is most likely to be triggered from thin or variable depth snowpack areas such as wind affected features, ridge crests, and near rocky outcroppings.
The same feature or path can slide repeatedly when the persistent weak layer gets reloaded with new snow.
Sunday night: Clear, moderate southwest wind, treeline low around -10 °C.
Monday: Sunny in the morning then increasing cloud cover with flurries, moderate southwest wind, treeline high around -3 °C.
Tuesday: Cloudy, up to 10 cm new snow, strong southwest wind gusting to extreme, treeline high around -2 °C.
Wednesday: Cloudy, 20-30 cm new snow, strong southwest wind gusting to extreme, treeline high around 0 °C.
On Saturday, numerous storm slabs up to size 2.5 were triggered by explosives.
A natural avalanche cycle to size 2 occurred overnight Thu-Fri with accumulating snowfall and wind. On Friday morning, explosives easily triggered storm slabs to size 2.5. Several natural slab avalanches of size 2 and one size 3 released naturally.
There has been an alarming pattern of large, persistent slab avalanches being consistently reported over the past two weeks. Almost all of these avalanches ran on the early December weak layer. Deeply buried persistent problems like these don't go away overnight, and it remains a serious concern.
15-30 cm of recent storm snow fell with southwesterly wind and warming temperatures, resulting in a denser slab forming over lower density snow. An accumulated total of 60-80 cm of new and recent snow now sits over variable and potentially weak snow surfaces including widespread facets, wind affected snow, and/or surface hoar up to 5 mm in sheltered areas.
The early December crust/facet layer has been responsible for sporadic but very large persistent slab avalanches over the past two weeks. The crust is now buried 120-200 cm deep except in thin, wind affected areas near ridgetops where nearly all of the recent avalanches have been triggered. We have uncertainty around whether new snow loads will cause this layer to fail naturally in the short term, or to help it heal in the longer term.
