Avalanche Forecast

Issued: Dec 19th, 2018 5:03PM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is considerable. Known problems include Deep Persistent Slabs and Storm Slabs.

kdevine, Avalanche Canada

South Rockies.

Natural avalanche activity has tapered off to some degree, but human triggered avalanches remain likely. Conservative terrain selection is recommended.

Summary

Confidence

Moderate.

Weather Forecast

WEDNESDAY NIGHT: Mainly cloudy with isolated flurries, up to 5 cm, moderate west to southwest winds, alpine low temperature near -9°c, freezing level 1000m. THURSDAY: Cloudy with flurries, 5-10 cm beginning to accumulate mid to late afternoon, southwest winds, 20-40 km/h, gusting to 80 km/h, alpine high temperature near -2, freezing level 1700m. FRIDAY: A mix of sun and cloud, west winds, 20-40 km/h, gusting to 90 km/h, alpine high temperature near -7°c, low temperature near -13°c, freezing level 1000m. SATURDAY: Cloudy with sunny periods and isolated flurries, west winds, 20-35 km/h, alpine high temperature near -10°c, low temperature near -15°c.

Avalanche Summary

Several explosives triggered size 2 avalanches on northeast aspects at 2200-2300m were reported in the region on Wednesday. Widespread natural activity was observed around Elkford and Sparwood on Tuesday. Many avalanches failed on deep persistent weak layers in the alpine. Snowmobiles remotely triggered several small avalanches below treeline on cutbanks north of Sparwood on Tuesday. Although these avalanches were small, they involved the entire depth of the snowpack and failed on weak layers at the base of the snowpack. See this MIN report. Deep persistent slabs were also reactive over the past few days. On Monday, a skier triggered a size 2 avalanche on an east aspect around 1800m. The avalanche failed on a persistent weak layer 40cm below the surface. On Friday and Saturday, explosive control produced numerous large (size 2-3) wind slab and deep persistent slab avalanches on north and east aspects above 2000m.

Snowpack Summary

25-60 cm of recent storm snow has formed storm slabs at upper elevations. This new snow substantially increases snowpack depths throughout the region, which prior to the storm ranged from 30-120 cm in the alpine and much less at lower elevations. The lower snowpack has a weak structure composed of facets and crusts, and the additional load of the new snow has pushed these weak layers past the tipping point. Any avalanche could step down to the bottom of the snowpack.

Problems

Deep Persistent Slabs

Any avalanche in the upper snowpack will likely step down to the weak snow at the bottom of the snowpack and produce large full depth avalanches.

Minimize overhead exposure; avalanches may reach the end of run out zones.Back off if you encounter signs of instability like whumphing, shooting cracks or recent avalanches.Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1.5 - 2.5

Storm Slabs

20-40 cm of new snow has left storm slabs primed for human triggering, especially on steep and wind loaded slopes.

If triggered the storm/wind slabs may step down to deeper layers resulting in large avalanches.Avoid freshly wind loaded features.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 2

Valid until: Dec 20th, 2018 2:00PM