Avalanche Forecast

Issued: Jan 28th, 2016 8:20AM

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

rbuhler, Avalanche Canada

South Rockies.

Recently formed wind slabs are expected to remain touchy on Friday. Conservative decision making remains critical in wind affected terrain.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

A weak ridge of high pressure should dry things out for Thursday night and Friday morning before a weak storm pulse arrives on Friday evening. 2-5 cm of new snow is expected by Saturday morning with freezing levels below 1000m. Alpine winds are expected to be light to moderate from the southwest. Lingering flurries are expected for Saturday with afternoon freezing levels around 1000m and light alpine winds from the west. Light flurries and cool temperatures are currently forecast to continue on Sunday.

Avalanche Summary

On Wednesday, a natural size 1.5 wind slab released in a cross loaded gulley with a 40cm slab thickness. Explosives also triggered a size 2.5 deep persistent slab avalanche on a south aspect at 2000m in the southeast of the region. This released down 70cm on the early December crust layer. No new avalanches were reported on Tuesday. Wind slabs are expected to remain reactive to human-triggering on Friday at higher elevations.

Snowpack Summary

Recent strong to extreme winds from the south to west have redistributed the snow at treeline and above. Wind slabs have formed on lee slopes and windward slopes are being stripped away. Moist surface snow is being reported to around treeline elevation on Thursday and a crust is expected to form over the weekend as freezing levels fall. The mid and lower snowpack has been settling well with the warm temperatures and is expected to gain considerable strength with several days of cooling. A weak crust/facet layer from early-December is typically down over 1m. It has become difficult to trigger this layer but it is still reactive in snowpack tests suggesting that if you are able to trigger it, the layer is capable of wide propagations and large destructive avalanches. Recent explosive control triggered a few large avalanches on this layer in the southeast of the region. In the northwest of the region, there may still be reactive surface hoar layers in the upper snowpack.

Problems

Wind Slabs

Recent strong winds from the south to southwest have formed touchy wind slabs in leeward features which are expected to remain reactive to human-triggering on Friday. Any cornices that formed recently may also be sensitive to triggering.

Use ridges or ribs to avoid pockets of wind loaded snow. >Be aware of the potential for wide propagations due to the presence of hard windslabs. >Avoid freshly wind loaded features. >

Aspects: North, North East, East, South East.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

Persistent Slabs

The likelihood of triggering a buried weak layer is slowly dropping but if triggered, these layers can still produce large, destructive avalanches. A cornice failure or a small avalanche in motion has the potential step-down to a deeper weak layer.

Use extra caution on steep open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.>Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

3 - 5

Valid until: Jan 29th, 2016 2:00PM