Avalanche Forecast

Issued: Dec 29th, 2011 9:31AM

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

swerner, Avalanche Canada

South Columbia.

Summary

Confidence

Fair - Intensity of incoming weather is uncertain on Friday

Weather Forecast

Friday: Snow amounts 10-15cms. Ridgetop winds 40km/hr from the West. Freezing levels could rise to 1000m. Saturday/Sunday: A ridge of high pressure is expected to move into the region for the weekend. A mix of sun and cloud with few flurries in the West. Mainly sunny skies in the Eastern part of the region. Temperatures should remain seasonal.

Avalanche Summary

Reports of natural large avalanches to size 3 have occurred throughout the South Columbias. Continued reports of rider triggered avalanches up to size 1.5, and natural cornice failures triggering slopes below up to size 2.5. The focus is on elevations between 1300-2100m, and mainly on North-South aspects. This avalanche cycle indicates that the December 24th surface hoar and the mid-December surface hoar layers have reached the tipping point and are producing large slab avalanches. Check out the Forecasters Blog to see an updated avi picture. It clearly indicates how touchy the surface hoar layer is on convexities and low angle terrain.

Snowpack Summary

The region has received storm snow amounts up to 50cms since December 26th. Wind slabs continue to form on North-South East aspects in the alpine and exposed treeline locations. New storm snow blankets elevations above 1100m. Below is receiving rain instead of the fluffy white stuff. In the upper meter of the snowpack two different weak layers exist. From the top down approx. 30-40cms lies the December 24th surface hoar layer. It has become very reactive over the past 24hrs in most locations across the region. Field tests show easy shears on this layer and Rutchblock 3 (Whole Block) scores. This layer can be found in sheltered areas at treeline and below. Going down 70-100cms is the mid-December surface hoar layer. This layer has naturally reached its threshold in the southern part of the region. In the Northern locations this layer is very sensitive and reactive to new loading from snow, wind, rain, and/or human trigger. This surface hoar layer is still producing sudden planar results in stability tests. These are the layers to watch. Below this sits a well consolidated, strong midpack.

Problems

Storm Slabs

Storm slabs can be destructive, run far and fast. The slabs are sitting on two weak layers in the upper 100cms of the snowpack. The weight of the slab may trigger the initial weakness, then step down to the deeper layer creating large avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 5

Wind Slabs

Consistent strong south westerly winds have blown around new snow and loaded open, lee slopes at treeline and in the alpine. You may even find wind effected snow in open areas below treeline.

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

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 5

Persistent Slabs

As the load increases the mid-December buried surface hoar layer may become reactive. The failure of this layer could initiate large, destructive avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

2 - 6

Valid until: Dec 30th, 2011 8:00AM