Avalanche Forecast

Issued: Jan 31st, 2013 9:12AM

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

Avalanche Canada swerner, Avalanche Canada

Summary

Confidence

Poor - Due to limited field observations

Weather Forecast

The next frontal system looks to be aimed at the North Coast for Friday bringing generally light precipitation amounts and rising freezing levels. The brunt of the frontal system will take affect through the weekend with temperatures dropping Sunday night.Friday: Light precipitation, snow amounts 5 cm above 1000 m. Ridgetop winds light from the SW. Alpine temperatures -1.0 and freezing levels near 1100 m. Saturday: No significant precipitation expected. Cloudy skies with ridgetop winds moderate from the South. Alpine temperatures around zero degrees with freezing levels rising to 1800 m. Saturday night into Sunday: The next wave of precipitation bringing light-moderate amounts. Ridgetop winds moderate from the south. Alpine temperatures dropping to -5.0 and freezing levels near 900 m in the afternoon falling to valley bottom overnight.

Avalanche Summary

Most recent avalanche activity shows the most recent surface hoar/facet/ crust layer (down 30-50 cm) becoming reactive remotely. This remote triggered avalanche was a size 2.0 slab avalanche (initiated 50 m away from the skier) at treeline elevation. Another report of a size 2.0 slab avalanche (skier triggered) also occurred. Both incidents were at 1200-1300 m on North aspects with crowns 50-60 cm deep, 30-40 m wide, and running up to 150 m in length.

Snowpack Summary

Recent storm snow (30-50 cm) is building over a variety of old surfaces including old wind slabs, scoured thin slopes, crusts and surface hoar. Wind slabs have built on lee slopes and behind terrain features and may be touchy to rider triggers.  Warmer temperatures have promoted some settlement and consolidated the recent snow into slab-like characteristics, and may have a poor bond. In some areas this layer has become reactive at treeline and below treeline elevations, under the weight of a person and remotely. With little observations from the field it's hard to get a good handle on how widespread this layer is. I stress the importance to dig down and become familiar with the snowpack in your neck of the woods. Look for, and test potential weak layers. Observe their reactivity before dropping into your run or line.The average snowpack depth at treeline is near 100 cm but remains quite inconsistent across the region. A strong mid-pack currently overlies a weak base layer of facets/depth hoar. Triggering of this basal weakness may still be possible from thin spots, rocky outcrops or under the weight of larger triggers such as cornice fall and larger amounts of new storm snow.

Problems

Wind Slabs

An icon showing Wind Slabs
New snow and strong shifting winds will build touchy wind slabs that are likely found behind terrain breaks such as ridges and ribs. Hollow sounds and cracking snow is a good indicator of unstable snow.
Avoid freshly wind loaded features.>Avoid cross loaded slopes at or above treeline.>Use ridges or ribs to avoid pockets of wind loaded snow.>

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 5

Persistent Slabs

An icon showing Persistent Slabs
Buried beneath the new snow sits a surface hoar/crust/facet weakness. This may be sensitive to rider triggers in steeper sheltered terrain or over convex rolls, especially at treeline and below treeline elevations.
Dig down to find and test weak layers before dropping into your line.>Whumpfing is direct evidence of a buried instability.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 5

Deep Persistent Slabs

An icon showing Deep Persistent Slabs
A deeply buried weak layer near the base of the snowpack could be triggered by large loads such as a cornice collapse or from a thin-spot trigger point.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 5

Valid until: Feb 1st, 2013 2:00PM