Avalanche Forecast

Issued: Jan 28th, 2018 5:05PM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is considerable. Known problems include Storm Slabs and Persistent Slabs.

Avalanche Canada cgarritty, Avalanche Canada

Incremental loading from new snow and winds are keeping the snowpack near a tipping point. Warm temperatures and rain will be another destabilizing factor on Monday.

Summary

Confidence

Moderate -

Weather Forecast

Sunday night: Cloudy with scattered flurries bringing 5-10 cm of new snow. Light to moderate southwest winds.Monday: Cloudy with continuing flurries bringing 5-10 cm of new snow, increasing overnight. Rain below about 1300 metres. Moderate southwest winds increasing over the day. Freezing level rising to 1700 metres with alpine high temperatures around -1 to 0.Tuesday: Mainly cloudy with isolated flurries and a trace of new snow. Light west winds. Freezing level to 1200 metres with alpine high temperatures of -4.Wednesday: A mix of sun and cloud. Light northwest winds. Alpine high temperatures of -7.

Avalanche Summary

Reports from Saturday showed explosives control in the Kootenay Pass area producing numerous storm slabs ranging from Size 2-2.5. Ski cutting in various areas in the region produced numerous 20-40 cm deep storm slabs generally from Size 1-1.5. A 15 cm deep mid-storm interface was noted for remote (from a distance) and sympathetic (by an adjacent release) triggering in the Rossland area.Explosive control near Nelson triggered numerous storm slab avalanches up to size 2 on Friday. On Wednesday, over a dozen natural size 2 storm slab avalanches were reported on all aspects and elevations, though most occurred at treeline and above. Additionally, several natural persistent slabs to size 2.5 were reported on northwest to easterly aspects above 1900m. These storm slabs and the persistent slabs beneath them are expected to remain reactive to human triggers.

Snowpack Summary

The snowpack in this region is currently being described as "Complex" and "Spooky".Another 10-20cm of new snow over Sunday night brings recent storm snow total to approximately 85-120 cm. Moderate southerly winds have been redistributing this new snow into storm slabs for several days.Currently, the primary layer of concern was buried in mid-January and is down around 70-100cm. It is composed of a mixture of surface hoar (weak, feathery crystals) and/or a crust. Numerous recent natural avalanches to size 2.5 have been reported on this sensitive layer and human triggering large, destructive avalanches on this layer remains likely.Below this layer lies a second crust/surface hoar interface buried early-January that is now 110-130 cm below the surface. The mid-December surface hoar layer is buried 120-150 cm below the surface. This layer still produces "sudden" test results and is most pronounced at treeline, but is also present below treeline . Two laminated crusts created by rain events in late November lay just below the mid-December interface, and may co-exist with facets.

Problems

Storm Slabs

An icon showing Storm Slabs
Forecast new snow and wind will continue to build touchy storm slabs at higher elevations on Monday. Rising temperatures and even rain will destabilize surface snow and promote loose wet avalanches at lower elevations - especially in steep terrain.
Use small slopes with low or no consequence to test the bond of the new snow.If triggered the storm slabs may step down to deeper layers resulting in large avalanches.Use extra caution on slopes if the snow is moist or wet and avoid terrain traps like gullies.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 2

Persistent Slabs

An icon showing Persistent Slabs
The snowpack is complex and has produced very large avalanches on up to four separate weak layers buried 60 to 140cm below the surface. A conservative approach and moderate-angled, simple terrain are good ways to manage a complex snowpack.
Be mindful that deep instabilities are still present and have produced recent large avalanches.Be aware of the potential for large avalanches due to the presence of buried surface hoar.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 3.5

Valid until: Jan 29th, 2018 2:00PM