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Avalanche Forecast

Archived

Dec 3rd, 2012–Dec 4th, 2012

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

Regions

Northwest Coastal.

Confidence

Poor - Due to limited field observations

Weather Forecast

A broad upper trough remains just offshore while a cooler, unstable onshore westerly flow has strengthened.  A multitude of systems will bring light –moderate precipitation, and strong SW winds. The region returns to normal seasonal temperatures, as the arctic air retreats.Tuesday: Freezing levels near 500 m, snow amounts 15-25 cm, ridgetop winds SW 50-70 km/hr, alpine temps -7.Wednesday: Freezing levels near 500 m, snow amounts 2-5 cm, ridgetop winds W 30 km/hr, alpin temps -9.Thursday: Freezing levels at the surface, snow amounts 5-10 cm, ridgetop winds SW 20 km/hr, alpine temps -11.

Avalanche Summary

On Sunday in the Shames area, a fairly large (no size was listed) natural avalanche had was seen on a North aspect initiating from the alpine just below the ridgeline. A couple skier triggered size 1.5 slab avalanches were reported from the same group skiing down from the Dome. The slab initiated as the second skier made a turn over a convex slope. The slab was 20-40 cm deep, 20-30 m wide and ran approx. 50 m down slope. For more information and observations from the area, please check out the Regional Forum Posts.

Snowpack Summary

Recent observations suggest that the alpine is fairly wind hammered from the steady, moderate SE winds. Hard slabs, storm, and wind slab instabilities exist at treeline and in the alpine. Recent test results done in the upper storm snow show an easy (RP) shear down 20-25 cm and a hard (RP) down 80 cm. The mid-pack is gaining strength and is well settled.Digging down deeper is the early November facet/crust layer. This crust sits near the base of the snowpack, and tests done in the Bear Pass area around 1100 m have shown this layer to be unreactive. Testing done in the Shames area on this interface have also shown no results, with moist snow below.Total snowpack depth is around 150-180 cm at treeline, and deeper but more variable in the alpine. The snowpack at below treeline elevations is near 100 cm deep, and reported to be strong.

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.

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.