Avalanche Forecast

Several more observations of recent persistent slab releases were observed on Sunday in the Norns and the Bonningtons. Two skier-triggered avalanches were also reported. Failure planes in all of these avalanches were identified as the early January layer discussed in our snowpack summary. 1700-2100 m was again the critical elevation band and east to northeast aspects figured prominently.

A widespread and reactive storm slab was reported around the region Friday and into Saturday. Skiers, vehicles, and explosives triggered slabs to size 2.5 with most crowns 30-50 cm deep, and many reported at treeline elevations 1700-2100 m (note poor visibility and no alpine observations). These avalanches were reported failing on the most recent interface or the early January crust/surface hoar layer about 10 cm lower. Wet loose avalanches were observed in below treeline terrain.

On Saturday and again on Sunday, explosives triggered a large (size 2.5) deep persistent slab avalanche (Saturday's report was from the western side of the Forecast region, which has received a bit more storm snow over the weekend, while Sunday's was in the Bonningtons). Both avalanches indicate our deep persistent layer remains reactive to large triggers at least.

Please continue to share any observations or photos on the Mountain Information Network.

Upper elevation storm snow totals since January 12 vary from 20-35 cm. This overlies a rain crust at lower elevations where recent precipitation fell as rain with freezing levels exceeding 1900 m. It overlies a mix of wind-affected and sheltered low density storm snow above about 1700 m.

At higher elevations, 50-60 cm of snow now sits on a layer of surface hoar from the start of January in wind-sheltered terrain, primarily around treeline. It has been identified as the failure plane in many recent avalanches in the region.

Another facet/crust layer is down 40-90 cm (and 2-10 cm thick at TL elevation). Below this the mid-pack is settled and consolidated.

A concerning and weak layer facets and crust 20-50 cm thick makes up the basal snowpack. Treeline snow depths average 150-210 cm.

Monday night

Cloudy with very isolated flurries. Light west or northwest winds.

Tuesday

Mainly cloudy. Light west winds. Treeline high temperatures around -4 C.

Cloudy with increasing flurries bringing less than 5 cm of new snow, continuing overnight. Light south winds. Treeline high temperatures around -4 C.

Decreasing cloud and easing flurries with about 5 cm of new snow from the overnight period. Light northwest winds. Treeline high temperatures around -4 C.

More details can be found in the Mountain Weather Forecast.

• Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
• Be aware of the potential for surprisingly large avalanches due to deeply buried weak layers.
• In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.