Avalanche Forecast

Issued: Feb 28th, 2019 3:54PM

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.

Recently formed wind slabs are sitting on top of buried wind slabs that are sitting on facets (weak, sugary snow). The fresh wind slabs may still be touchy and the buried wind slabs are remaining reactive to human triggers longer than is typical.

Summary

Confidence

High - The weather pattern is stable

Weather Forecast

THURSDAY NIGHT: Cloudy / Light, northwesterly winds / Alpine low -17.FRIDAY: Mostly cloudy with sunny periods / Light to moderate, northwesterly winds / Alpine high -17.SATURDAY: Sunny / Light, northeasterly winds / Alpine high -21.SUNDAY: Sunny / Light, northeasterly winds / Alpine high -17.

Avalanche Summary

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 at lower elevations below treeline. They are likely 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

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 mid-January. They are approximately 40- 60 cm and 60-80 cm below the surface. 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 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

Buried, hard wind slabs that often become unreactive after a few days continue to surprise riders. Thin to thick rocky areas are likely places to trigger these.

Avoid wind loaded pockets, especially near ridge crests and roll-overs.Avoid 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 - 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 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

2 - 3

Valid until: Mar 1st, 2019 2:00PM