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

South Columbia.

The region holds a tricky mix of long-lived wind slab and persistent slab problems, with new snow instabilities to manage in the south. Be mindful of how this mix changes by elevation and by location.

Summary

Confidence

High -

Weather Forecast

Sunday night: Clear. Light northeast winds.Monday: Sunny. Light east or 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 with cloud increasing over the day and flurries overnight. Light to moderate east winds. Alpine high temperatures around -8.

Avalanche Summary

Observations from the past few days have shown size 1-2 wind slabs releasing with skier traffic on a range of aspects at ridgetop, most recently on southwest aspects (lee of recent northeast winds). A few storm slabs were reported in the south of the region where up to 30 cm of snow fell at the end of the week. Small (size 1-1.5) loose dry avalanches have also been observed releasing naturally from steeper, sun exposed slopes. Persistent slab avalanche activity on the mid-January weak layer has slowed down, but not stopped. The most recent report of a persistent slab was from yesterday on a west aspect at 2300 m in the Meadow Creek area. This layer has evolved a low likelihood, high consequence avalanche problem at treeline and below. Check out the great photos from a recent MIN. Take note of the low angle terrain, treeline elevation, and the light load of a single ski track that triggered this avalanche.

Snowpack Summary

Spotty convective flurries brought up to 30 cm of low density new snow to a few areas in the south of the region at the end of the week. This new snow likely overlies sun crust on sun-exposed aspects. Below any new snow, strong ridge-top winds (most recently from the northeast) have created wind slabs on all aspects at upper elevations. These wind slabs have shown prolonged reactivity because of the faceted (weak, sugary snow) they overlie. There are two prominent weak layers in the upper snowpack that were buried in mid and late January. They can be found between 40-90 cm below the surface. These layers consist of surface hoar (weak, feathery crystals) and may be associated with crusts on steeper, south facing slopes. These weak layers have been most prominent and most reactive at lower elevations - 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

Recent wind slabs can be found on all aspects and new snow is available to redistribute into fresh slabs in the south of the region. Wind slabs have been showing prolonged reactivity due to the weak, faceted snow they sit on.

Avoid wind loaded pockets near ridge crests and back off from slopes that feel hollow or drum-like.Steep and rocky terrain are likely places to trigger buried wind slabs.Forecast northeast winds will focus new slab formation on southwest aspects.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Persistent Slabs

Reports of persistent slab avalanches are becoming less frequent, suggesting a lower likelihood, but high consequence avalanche problem focused at lower elevations. This problem requires discipline and careful terrain selection to manage effectively.

Use conservative route selection; choose moderate angled terrain with low consequence.Avoid low elevation cut-blocks where this layer is well preserved.Avoid 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 4th, 2019 2:00PM