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Avalanche Forecast

Archived

Dec 4th, 2019–Dec 5th, 2019

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

Regions

Cariboos.

Storm snow totals have varied across the region, with field observations reporting deeper layers in the snowpack being becoming more reactive. Conservative terrain choice is recommended until the distribution of weak layers is better understood.

Confidence

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

Wednesday night: Cloudy with periods. Alpine temperature -10 C, west wind 10-25 km/hr.

Thursday: Cloudy with sunny periods and isolated flurries. Alpine temperature -9 C, southwest wind 10-20 km/hr.

Friday: Snow, 10-25 cm. Alpine temperature -10 C, southwest wind 20-35 km/hr.

Saturday: Snow and flurries, 5-10 cm. Alpine temperature -6, west wind 20-40 km/hr.

Avalanche Summary

On Wednesday, storm snow continued to be reactive to skier traffic, including triggering slab avalanches to size 2 and cracking on small, supported slopes. A couple of field observations reported slab avalanches failing on a layer of surface hoar (down 50-80 cm) at treeline elevations.

On Tuesday, a natural avalanche cycle was observed in Glacier National Park. Numerous size 2 storm slab avalanches were observed on all aspects at 2200 m and above. Additionally, 2 size 3 storm slab avalanches were observed on a north aspect at 2165 m and a northwest aspect at 2400 m. Near Revelstoke, storm slab avalanches to size 2 were reacting easily to explosives, many occurring on north and northeast aspects from 1800-2300 m.

Snowpack Summary

Storm snow totals reached 20-40 cm along with moderate westerly winds. Slabs have formed in areas exposed to wind.

The new snow covered a faceted upper snowpack and previously wind-affected surfaces, and surface hoar in sheltered areas around treeline and below.

Below the 15-40 cm layer of old, wind affected snow, a layer of surface hoar (feathery crystals) may be found in sheltered areas around treeline. In these areas old, stubborn wind slabs may still be reactive where they overly the weak surface hoar on a crust.

A variety of crusts from late October are buried deeper in the snowpack.

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.