Avalanche Forecast

Issued: Dec 4th, 2012 9:02AM

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

swerner, Avalanche Canada

Northwest Inland.

Limited field observations and reports exist from this region. Conditions may be variable. It is important to be familiar with the snowpack and avalanche problems that may exist in your local mountains.

Summary

Confidence

Poor - Due to limited field observations for the entire period

Weather Forecast

An upper level trough will influence an onshore flow with several embedded systems. These systems will bring light-moderate amounts of precipitation. Winds will generally stay light and freezing levels will remain in valley bottoms through the forecast period.Wednesday: Snow amounts 5-8 cm, ridgetop winds W 35 km/hr, alpine temps near -10.Thursday: Snow amounts 5 cm, ridgetop winds SW 25 km/hr, alpine temps near -11.Friday: Snow amounts near 5 cm, ridgetop winds SW 10 km/hr, alpine temps near -12.

Avalanche Summary

Recent reports of several loose, dry sluffs size 1.5 from steep, rocky terrain features running mid-path on Northerly aspects. For a bit more information in the Hankin Area, check out the Regional Forum Posts.

Snowpack Summary

Wind slab instabilities exist in the upper snowpack at treeline and in the alpine. They may be touchy to rider triggers; especially on leeward slopes and behind terrain features where pockets of wind slab easily build. At treeline depths in the southern part of the region range between 90-125 cm, but highly variable in the alpine with deep wind drifts and scoured slopes in exposed areas. At treeline spotty, isolated areas of surface hoar growth exists (up to 3mm). Recent snowpack tests on a SE aspect around 1400mÂ showed CTH (resistant "pop") on an old facet layer 55 cm down, and a rutschblock score of 5. Generally, the mid-pack is gaining strength and possibly even bridging the persistent weakness below. Digging down deeper is the early November facet/crust persistent layer. This crust sits near the base of the snowpack down 80-130 cm. Test results on this layer earlier this week produced hard results ("drops"). I have no current observations to suggest the snow above or below this interface is gaining strength, or weakening. In most areas, because this weakness is located near the ground, any associated avalanche activity will likely be limited to slopes with smooth ground cover.

Problems

Wind Slabs

New storm slabs and wind slabs have formed; especially on lee slopes, gully features, and behind ridges. Natural avalanche activity is likely with continued loading. Rider triggering is likely, especially on steep convex slopes.

Avoid freshly wind loaded features.>Whumpfing, shooting cracks and recent avalanches are all strong indicators of an unstable snowpack.>

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

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 4

Persistent Slabs

Basal facet/crust weaknesses are often prone to remote triggering and step down avalanches. Typical trigger points include thin rocky areas. They may be difficult to trigger, but deep persistent slab avalanches are often very large.

Be aware of thin areas that may propagate to deeper instabilites.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 6

Valid until: Dec 5th, 2012 2:00PM