Avalanche Forecast

Issued: Mar 2nd, 2019 4:47PM

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.

Be mindful of the persistent slab problem lingering at lower elevations as you search for snow that has been sheltered from recent winds.

Summary

Confidence

High -

Weather Forecast

Saturday night: Clear. Light northeast winds. Sunday: Sunny. Light northeast winds. Alpine high temperatures around -16.Monday: Sunny. Light northeast winds. Alpine high temperatures around -11.Tuesday: Sunny. Light east winds. Alpine high temperatures around -9.

Avalanche Summary

Reports from Thursday show a continuation of wind slabs reacting to ski cuts, with a trend toward smaller (size 1) releases. Larger and older buried wind slabs remain a concern for the weak faceted grains they sit above. 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. Expect these wind slabs to remain reactive to human triggers where they are sitting on facets.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 that was buried mid January. This layer has created a low likelihood, high consequence scenario that requires discipline and careful terrain selection to manage effectively.

Snowpack Summary

Recent strong northeasterly ridge-top winds have created wind slabs on lee features at treeline and above. Below this wind affected layer, older buried wind slabs exist on a variety of aspects. These remain a concern for overlying facets (weak, sugary snow), causing them to remain reactive for longer than is typical for a wind slab problem.There are two prominent weak layers in the upper snowpack. One was buried at the end of January, and the other mid-January. They are approximately 40-60 cm and 60-80 cm below the surface, respectively. 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. Below them, hard, buried wind slabs on all aspects have shown prolonged reactivity due to the weak, faceted snow they sit above.

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

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

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Unlikely - Possible

Expected Size

1.5 - 2.5

Valid until: Mar 3rd, 2019 2:00PM