Avalanche Forecast

Issued: Feb 20th, 2018 5:16PM

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

mgrist, Avalanche Canada

South Columbia.

Strong winds formed reactive wind slabs and cornices at ridge crests. The sun is packing a punch these days and can trigger avalanches. Riding preserved powder in sheltered trees is a good option.

Summary

Confidence

Moderate - Wind effect is extremely variable

Weather Forecast

Cloudy Wednesday then clear and cold until light snow arrives on Friday. Overnight lows near -20 Celsius in some locations. WEDNESDAY: Cloudy with isolated flurries possible. Tree line temperatures around -14 Celsius. Winds moderate westerly 20-30 Km/hr.THURSDAY: Sunny with cloudy periods. Tree line temperature around -12 Celsius. Winds light northerly 15 Km/hr.FRIDAY: Light snow (5-10 cm possible) . Tree line temperature around -10 Celsius. Moderate southwest winds 20-30 Km/hr.

Avalanche Summary

On Monday, several natural wind slab avalanches to size 3 were reported on a wide range of aspects above 2100m. On Sunday we received reports of several wind slab avalanches to size 2, on a wide range of aspects. See here for a good example in the MIN report. 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, with a higher frequency in the south east of this region.

Problems

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.Be careful with wind loaded pockets, especially near ridge crests and roll-overs.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Persistent Slabs

Several troublesome layers exist in the snowpack and may be reactive to large triggers such as a cornice or storm slab release. Activity seems to be more prevalent in the south east corner of the region.

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 21st, 2018 2:00PM