Avalanche Canada triley, Avalanche Canada

Sea to Sky Avalanche Forecast

Dec 5th, 2012 8:55AM

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

Summary

Confidence

Fair - Due to limited field observations for the entire period

Weather Forecast

Overnight and Thursday: Mostly cloudy with light precipitation overnight. Mostly dry with some sunny breaks during the day. Some western upslope areas may see 3-5 mm in the morning. Moderate westerly winds and temperatures near -10.0 in the alpine.Friday: Some light precipitation overnight. Sunny periods during the day with moderate west – southwest winds, gusty periods in the evening. Alpine temperatures continue to be about -10.0Saturday: Sunny periods with light winds and alpine temperatures about -7.0

Avalanche Summary

Some size 1.0  stiff wind slab releases in the alpine on Monday. Very strong winds during the storm stripped fetch zones and transported snow well down lee slopes.

Snowpack Summary

Treeline and alpine areas have received well over a metre of new snow since late last week with weaknesses lingering within and under this storm snow. Of particular note was preserved 8mm surface hoar found on a sheltered open slope just below treeline, which gave moderate but energetic sudden collapse results in repeated compression tests. The mid-pack seems to be fairly settled, strong, and possibly bridging instabilities that may exist deeper. However, snowpack tests continue to produce occasional hard but sudden results on the early November facet/crust combination down as deep as 200cm on leeward slopes. Furthermore, favorable slab structure for step-down fractures can contribute to the persistence of this deep weakness.

Problems

Wind Slabs

An icon showing Wind Slabs

Likelihood

Likely

Expected Size

2 - 5
Fresh wind slabs can be found well below ridge crests, behind terrain features and in cross-loaded gullies in any wind-exposed terrain. Expect these deep drifts to be very touchy.
Avoid freshly wind loaded features.>Be aware of the potential for wide propagations due to the presence of hard windslabs.>

Aspects:

North, North East, East, South East.

Elevations:

Alpine, Treeline.

Storm Slabs

An icon showing Storm Slabs

Likelihood

Likely - Possible

Expected Size

2 - 5
Weaknesses within and under the recent storm snow are susceptible to human triggers, particularly in sheltered areas treeline and below, and could easily produce avalanches large enough to bury a person.
The new snow will require several days to settle and stabilize.>

Aspects:

All aspects.

Elevations:

All elevations.

Persistent Slabs

An icon showing Persistent Slabs

Likelihood

Possible - Unlikely

Expected Size

2 - 6
An old facet/crust combination deep in the snowpack may wake up with heavy triggers, smaller avalanches stepping down, or triggering from thin-spots, particularly on slopes with smooth ground cover.
Be aware of thin areas that may propagate to deeper instabilites.>Be aware of the potential for full depth avalanches due to deeply buried weak layers.>

Aspects:

All aspects.

Elevations:

Alpine, Treeline.

Valid until: Dec 6th, 2012 2:00PM