Avalanche Forecast

Issued: Dec 21st, 2017 8:00AM

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

Parks Canada percy woods, Parks Canada

A reactive persistent weak layer of surface hoar down 40cm resides below surface layers.  Take time to evaluate the snowpack as you transition into avalanche terrain.

Summary

Weather Forecast

Mainly cloudy today with flurries and light SW wind. Alpine temperatures should reach -11C. Sunny with cloudy periods through the weekend with daytime highs in the -15 to -17C range and light northerly winds.

Snowpack Summary

40cm of storm snow sits on top of the Dec 15 surface hoar/persistent weak layer. On steeper solar aspects this layer is a crust and/or a crust with small surface hoar on top. The crust runs well up into the alpine on steep south aspects. Deeper in the pack there are a series of crust layers that are currently well bonded to neighboring layers.

Avalanche Summary

6 natural avalanches to size 2.5 off the north face of Mt MacDonald before control yesterday. Avalanche control east of Rogers Pass summit produced avalanches up to size 3 with most slides in the size 2 range. These slides were confined to the recent dry storm snow running far and fast. Slides lost momentum where they ran into old avalanche debris.

Confidence

Due to the number and quality of field observations

Problems

Persistent Slabs

An icon showing Persistent Slabs
Recent storm snow is shifting into a settled persistent slab. Expect the slab to be increasingly sensitivity as you transition into wind effected terrain. Steeper solar slopes harbor a thin crust layer below slab and a facet surface hoar combo BTL.
Watch for whumpfing, hollow sounds, and shooting cracks.Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 3

Wind Slabs

An icon showing Wind Slabs
Mod gusting to strong N-NE winds Tuesday formed reverse loaded windslab in wind exposed areas at and above treeline. These slabs may have surface hoar or crust underneath leading them to be sensitive to human triggering.
Keep an eye out for reverse loading created by N-NE winds earlier in the week.Watch for signs of instability such as whumpfing, or cracking.

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 3

Valid until: Dec 22nd, 2017 8:00AM