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Avalanche Forecast

Archived

Dec 29th, 2011–Dec 30th, 2011

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

South Columbia.

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 Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.