Avalanche Forecast

Issued: Feb 18th, 2018 5:01PM

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

Avalanche Canada mgrist, Avalanche Canada

Strong winds created reactive wind slabs at higher elevations. Riding preserved powder in sheltered trees is a good option.

Summary

Confidence

Moderate - Wind effect is extremely variable

Weather Forecast

Clear and cold for the foreseeable future, with overnight lows near -22 Celsius in some locations. Monday: Mainly sunny with increasing cloud in the afternoon. Tree line temperature around -13 Celsius. Winds light northerly.Tuesday: Cloudy with sunny periods. Tree line temperature around -12 Celsius. Light winds northerly. Wednesday: Cloudy. Tree line temperatures around -12 Celsius. Winds light to moderate westerly.

Avalanche Summary

On Sunday we received reports of several wind slab avalanches to size 2, on a wide range of aspects. On Saturday explosives control work produced several storm slab avalanches to size 2.5 on a wide variety of aspects near tree line. In Rogers Pass a week ago, skiers remotely triggered a size 3.5 persistent slab avalanche from 40 m away on a south-facing, cross-loaded slope at 2600 m. On the same day, a helicopter remotely triggered a size 3 persistent slab avalanche on a similar aspect / elevation in the Selkirks a little closer to Revelstoke. Although deeper, persistent avalanche activity is becoming less frequent, these recent avalanches point to the continued reactivity and destructive potential of these layers.

Snowpack Summary

40-60 cm of recent storm snow has settled into a slab in the upper snowpack. Strong winds, most recently from the north / east, shifted these accumulations into deeper, reactive slabs in wind-exposed terrain. These accumulations overlie a mix of older wind slabs in exposed higher elevation terrain, a sun crust on steep solar aspects, a rain crust below 1600m and surface hoar on sheltered slopes.Below the snow surface several persistent weak layers make up a troublesome snowpack. In the top 1.5-2.5 m of the snowpack, two surface hoar/ crust layers buried in January can be found. Expect to find one or the other of these on all aspects and elevations.Deeper in the snowpack (around 200 cm deep) is a facet/crust/surface hoar layer from December, most prevalent at and below tree line.Near the base of the snowpack is a crust/facet combo, most likely to be triggered from thin spots in the alpine.All of these layers have produced large avalanches recently. The wide distribution and ongoing reactivity of these layers suggests that avoidance through choosing simple terrain is the best strategy.

Problems

Wind Slabs

An icon showing Wind Slabs
Watch for wind slab development on south through west aspects due to 'reverse loading' from strong winds blowing from the north / east.
Use ridges or ribs to avoid pockets of wind loaded snow.If triggered the storm/wind slabs may step down to deeper layers resulting in large avalanches.Avoid recent wind loaded areas until the slope has had a chance to stabilize.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2.5

Persistent Slabs

An icon showing Persistent Slabs
Several troublesome layers exist in the snowpack and may be reactive to large triggers such as a cornice or storm slab release. Human triggering may also be possible in shallow or thin, rocky areas.
Avoid steep convexities or areas with a thin or variable snowpack.Avoid the runout zones of avalanche paths. Very large avalanches have been running full path.Pay attention to overhead hazards like cornices which could easily trigger persistent slabs.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 4

Valid until: Feb 19th, 2018 2:00PM