Avalanche Forecast

Friday night: Tapering snowfall and flurries, up to 10 cm. Moderate W wind. Treeline low around -15 °C. 

Saturday: Mostly cloudy with isolated flurries. Moderate WSW wind. Treeline high around -6 °C. 

Sunday: Mix of sun and cloud. Moderate to light SW wind. Treeline high around -3 °C. 

Monday: Sunny. Light and increasing S wind. Treeline high around -3 °C. 

A natural avalanche cycle to size 2 occurred overnight Thurs-Fri with accumulating snowfall and wind. On Friday morning, explosives easily triggered storm slabs to size 2.5.

On Wednesday, wind slabs were reactive to explosives up to size 2 in the west of the region. On Monday and Tuesday, storm slab avalanches were reactive naturally and to skier and explosive triggers, up to size 2.

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. Additional loading by the weight of new snow will further stress this weakness and may result in a resurgence of reactivity.

• On Tuesday, explosive control work near Rossland produced a size 2.5 persistent slab avalanche on a layer of surface hoar from late December. 
• On Monday in the neighboring South Columbia region, a natural size 2.5 persistent slab avalanche was reported on a NE aspect at 2200 m failing 80 cm deep on the early December layer.
• A few notables from last week feature in our latest blog Photos of recent persistent slab avalanches in the southern interior. 

20-50 cm of new snow accumulated by the end of Friday was accompanied by southwesterly wind and warming temperatures. An accumulated total of 70-100 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, which may make for a weak bond at this interface.

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 over 1 m 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.

• Give the new snow time to settle and stabilize before pushing into bigger terrain.
• Caution around convexities or sharp changes in terrain.
• Be aware of the potential for large avalanches due to the presence of a persistent slab.