Avalanche Forecast

Issued: Feb 27th, 2019 4:07PM

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.

jsmith, Avalanche Canada

North Columbia.

Fresh wind slabs are sitting on top of buried wind slabs that are sitting on facets (weak, sugary snow). The fresh wind slabs are touchy and the buried wind slabs may remain reactive to human triggers longer than is typical for this region.

Summary

Confidence

High - The weather pattern is stable

Weather Forecast

WEDNESDAY NIGHT: Clear / Light, northeasterly winds / Alpine low -10.THURSDAY: Sunny / Light, northeasterly winds / Alpine high -9.FRIDAY: Mix of sun and cloud / Light to moderate, northwesterly winds / Alpine high -16.SATURDAY: Sunny / Light, northeasterly winds / Alpine high -19.

Avalanche Summary

On Tuesday, numerous natural and human triggered wind slab avalanches up to size 1.5 were reported on primarily north aspects at treeline and above. Additionally, a human triggered size 1.5 persistent slab avalanche was reported on a north aspect at 1400 m. near frisby ridge.Over the past week there have been numerous reports of persistent slab avalanches, some of which were human triggered. They have been large avalanches (size 2-2.5), occurring on a variety of aspects at treeline and below treeline elevations. They are likely failing on the persistent weak layer of surface hoar and/or crusts that were buried mid January. These layers have created a low likelihood, high consequence scenario that requires discipline and careful terrain selection to manage effectively.

Snowpack Summary

Strong northeasterly ridge-top winds have created fresh wind slabs on lee features at treeline and above. Additionally, there are buried wind slabs on a variety of aspects that are sitting on facets (sugary snow) which may cause them to remain reactive to human triggers longer than what is typical for a wind slab problem in this region.There are two prominent weak layers in the upper snowpack. One was buried at the end of January, and the other was buried mid January. They are approximately 40 and 75 cm below the surface. Both layers consist of a mixture of surface hoar (weak, feathery crystals) and facets (sugary snow), which likely also sit on a sun crust on steep, south facing slopes. These weak layers are most prominent at treeline and below treeline elevations.Very sporadically, failures have occurred near the base of the snowpack in this region, or in neighboring regions. These avalanches have primarily been in steep, rocky, high alpine areas with a shallow snowpack.

Problems

Wind Slabs

Steep and rocky terrain are likely places to trigger buried wind slabs.Avoid 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

Likely

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 are slow to change and have created a low likelihood, high consequence scenario in the snowpack.

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

2 - 3

Valid until: Feb 28th, 2019 2:00PM