Avalanche Forecast

Issued: Mar 6th, 2017 5:34PM

The alpine rating is moderate, the treeline rating is moderate, and the below treeline rating is low. Known problems include Wind Slabs and Deep Persistent Slabs.

mgrist, Avalanche Canada

Northwest Inland.

Several days of cold benign weather. Concerns include wind slabs at higher elevations and the ongoing potential to trigger deep persistent slabs in shallow snowpack areas.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

We're looking at isolated flurries and cool temperatures throughout the forecast period. TUESDAY: Flurries with 2-5 cm possible, 20-40 km/h southeast winds, alpine temperatures around -15 C. WEDNESDAY: Isolated flurries, 20-30 km/h east winds, alpine temperatures around -18 C. THURSDAY: Cloudy with scattered flurries and up to 3-5 cm of new snow, 30-50 km/h east winds, alpine temperatures around -20 C.

Avalanche Summary

On Saturday, skiers were able to remote-trigger a storm slab (Size 1.5) on a north aspect at 1800m in the northern part of the region.On Friday, several size 1-2 natural wind slabs were reported in both the Telkwas and Sinclair areas on north and east aspects. The avalanches likely occurred during the storm on Thursday. A few small size 1 slab and loose dry avalanches running on a crust were skier triggered in steep low elevation terrain.Isolated wind slabs may still be found in alpine locations on leeward slopes behind terrain features.

Snowpack Summary

We've had up to 6cm of snow since Saturday, bringing recent storm snow totals to 15-45 cm. In some areas wind effect at higher elevations resulted in wind slabs on east and north aspects. The new snow buried a variety of old snow surfaces including stiff wind slabs, facets, crusts and surface hoar. The new snow may have a poor bond to these interfaces, especially in places where the slab is stiffer and more cohesive due to winds.At treeline, the average snowpack depths are 120-190 cm and a well consolidated mid-pack of approximately up to 100 cm sits above weak basal facets (sugary snow) near the ground. Recent snowpack testing has shown sudden easy results down 25 cm on a surface hoar layer and sudden hard results down 100 cm within the faceted snow. The deeper basal weakness remain a concern, especially in thin rocky start zones and shallow snowpack locations.

Problems

Wind Slabs

Gusty southwest winds at upper elevations have formed fresh wind slabs on leeward slopes and behind terrain features. Loose dry avalanches may be easily triggered below treeline or in areas sheltered from the wind.

Sheltered slopes will likely offer the best skiing today.Use ridges or ribs to avoid pockets of wind loaded snow.

Aspects: North, North East, East, South East, South.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 3

Deep Persistent Slabs

A lingering weakness at the bottom of the snowpack may remain sensitive to human triggering, especially in shallow snowpack areas. Smaller avalanches in motion also have the potential to step down and trigger deep persistent slabs.

Avoid steep convexities or areas with a thin or variable snowpack.Be aware of the potential for full depth avalanches due to weak layers at the base of the snowpack.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

Valid until: Mar 7th, 2017 2:00PM