Avalanche Forecast

Issued: Jan 20th, 2015 8:38AM

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

jfloyer, Avalanche Canada

Purcells.

Safe backcountry travel requires caution and good terrain selection at this time.

Summary

Confidence

Good

Weather Forecast

Wednesday: Dry. Freezing level around 1000 m. Ridgetop winds 30-40 km/h from the southwest. Thursday: Light flurries. Freezing level around 1500 m. Ridgetop winds around 30 km/h from the southwest. Friday: At present this region looks like it will stay mostly dry, but models are uncertain with an approaching storm that could bring some snow and/or rain to this region. Strong southwest winds and rising freezing levels likely.

Avalanche Summary

Avalanches up to size 2 were reported to have run during and immediately after the most recent storm on all aspects and at elevations from 1800-2300 m. Most avalanches were running on the most recent layer of surface hoar, with typical crown depths of 30-60 cm. There was one report of an avalanche on the more deeply buried mid-December weak layer, although it appears as though it may have been triggered in a shallow spot, as the crown depth was reported to be only 30-45 cm.

Snowpack Summary

Between 15cm and 40cm of recent snowfall has buried widespread 10-20mm surface hoar and a sun crust on steep sun exposed slopes. Strong winds have blown these accumulations into deeper deposits in higher elevation terrain. Due to the underlying surface hoar, I would expect continued touchy conditions, especially in areas where the recent snowfall exists as a cohesive slab.The mid-December surface hoar/crust layer is typically down 60-120cm below the surface. The reactivity of this persistent weak layer appears to be quite variable but still has the potential for large, destructive avalanches in some areas. The layer appears to be the most reactive at and below treeline. The mid-Nov weak layer is near the bottom of the snowpack but has generally become inactive.

Problems

Persistent Slabs

A weak layer comprising of feathery surface hoar crystals and on south aspects a crust is buried between 25 and 45 cm below the surface. This layer appears to be widely found in this region and many recent avalanches were triggered on it.

Choose well supported terrain without convexities.>Whumpfing, shooting cracks and recent avalanches are all strong inicators of unstable snowpack.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 4

Wind Slabs

Winds were very strong during the last storm and created dense areas of wind slab in the lee of ridges and terrain breaks.

Be cautious as you transition into wind affected terrain.>Stay off recent wind loaded areas until the slope has had a chance to stabilize.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 3

Deep Persistent Slabs

A weak layer buried mid-December is still producing dangerous avalanches over a month after it was first buried. Particularly for slopes around treeline, there is a danger for a small avalanche to step down to this layer increasing the consequences.

Avoid open slopes and convex rolls at treeline where buried surface hoar may be preserved.>Be aware of thin areas that may propogate to deeper instabilites.>

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

3 - 5

Valid until: Jan 21st, 2015 2:00PM