Avalanche Forecast

Issued: Mar 3rd, 2019 4:42PM

The alpine rating is moderate, the treeline rating is moderate, and the below treeline rating is moderate. Known problems include Wind Slabs and Persistent Slabs.

cgarritty, Avalanche Canada

North Columbia.

Avoiding wind-affected upper elevations is likely to lead you toward sheltered lower elevations where a tricky persistent weak layer may be well preserved. Manage the uncertainty here by seeking out lower angle, lower consequence slopes.

Summary

Confidence

High -

Weather Forecast

Sunday night: Clear with cloudy periods. Light northeast winds.Monday: Mainly sunny. Light northeast winds. Alpine high temperatures around -11.Tuesday: Sunny with cloudy periods. Light east winds. Alpine high temperatures around -10.Wednesday: A mix of sun and cloud. Light east winds. Alpine high temperatures around -9.

Avalanche Summary

Reports from the past couple of days show a continuation of wind slabs reacting to ski cuts, with a trend toward smaller (size 1) releases. Small (size 1-1.5) loose dry avalanches have also been observed releasing naturally from steeper, sun exposed slopes in recent days.On Wednesday, numerous rider triggered wind slab avalanches up to size 2 were reported primarily on northerly aspects at treeline and above. The largest one was a buried, hard wind slab that was sitting on facets on top of a crust. Over the past week there have been several reports of human triggered persistent slab avalanches. They have been large avalanches (size 2-2.5), occurring on a variety of aspects, primarily below treeline. These have been failing on the persistent weak layer of surface hoar and/or crust described in our snowpack summary. This layer has created a low likelihood, high consequence scenario that requires discipline and careful terrain selection to manage effectively.

Snowpack Summary

Weeks of mainly dry, windy, and cold weather have transformed the snowpack at upper elevations into a mix of wind-affected surfaces and wind slabs of varying ages on all aspects. These wind slabs have shown prolonged reactivity because of the faceted (weak, sugary snow) they overlie. There are a couple of prominent weak layers in the upper snowpack that were buried in mid and late January. These can be found approximately 40-80 cm deep. Both layers consist of surface hoar (weak, feathery crystals) and may be associated with a crust on steep, south facing slopes. These weak layers have been most reactive at lower elevations, and especially below treeline.The lower snowpack is generally considered to be strong, except for shallow, rocky areas where the cold temperatures continue to facet (weaken) the snowpack.

Problems

Wind Slabs

Recently formed wind slabs can be found on all aspects, but especially to the lee of recent northeast winds. These wind slabs have shown prolonged reactivity due to the weak, faceted snow they sit above.

Steep and rocky terrain are likely places to trigger buried wind slabs.Back off from slopes that sound hollow or drum-like.Avoid wind loaded pockets, especially near ridge crests and roll-overs.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Persistent Slabs

There are two persistent weak layers in the snowpack, buried approximately 40 cm and 75 cm below the surface. These layers have been slow to heal and have evolved into a low likelihood, high consequence avalanche problem focused at lower elevations.

Avoid convexities as well as steep, open and/or sparsely treed slopes at and below treeline.Use conservative route selection, choose moderate angled terrain with low consequence.Avoid low elevation cut-blocks where this layer is well preserved.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Unlikely - Possible

Expected Size

1.5 - 2.5

Valid until: Mar 4th, 2019 2:00PM