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Avalanche Forecast

Archived

Dec 30th, 2011–Dec 31st, 2011

Alpine
Natural and human triggered avalanches likely.
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 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.

Regions

South Columbia.

Confidence

Good - -1

Weather Forecast

One last pulse out of the recent active weather system will affect the region Friday evening before a strong ridge of high pressure anchors itself over Eastern BC for the weekend. Skies clear and cooler temperatures pervade under the ridge which will bring freezing levels down to valley bottom. On Saturday you can expect moderate winds out of the W and a daytime high of -9 with overnight lows dropping slightly to -12. A weakening system slides into the region Monday bringing light precipitation and cloudy skies.

Avalanche Summary

Reports of natural large avalanches up 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

Up to 100 cm have fallen across the region since Boxing Day. This meter of snow sits on top of a weak layer that is widespread across the region; the mid December surface hoar/facet/crust combination. In tests this layer fails with sudden planer characteristics meaning that the failure has a lot of energy in it. This layer can be found at all three elevation bands and is still quite active. This layer will continue to be reactive to increased load in form of snow, rain, wind or a recreating human. Below the mid December weak layer lies a well consolidated & strong mid pack.

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.