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Avalanche Forecast

Archived

Dec 5th, 2012–Dec 6th, 2012

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

Regions

Northwest Inland.

Confidence

Poor - Timing, track, or intensity of incoming weather is uncertain on Saturday

Weather Forecast

Thursday: The region will be under the influence of a Westerly zonal flow. This will bring cooler temperatures, mainly cloudy skies and continuous light-moderate snow, alpine temps -10, ridgetop winds SE 30km/hr. Friday through Saturday: A weak low pressure system moves into the region bringing moderate snow, ridgetop winds NW 15 km/hr, and alpine temps near -11.

Avalanche Summary

Recent reports of several isolated loose dry sluffs from steep terrain features. For a bit more information in the Hankin Area, check out the Regional Forum Posts.

Snowpack Summary

Wind slab instabilities are likely to 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. Treeline depths 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). This is most likely buried down 15-20 cm under the recent storm snow. Snowpack tests on a SE aspect around 1400m  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 deep 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.

Problems

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.