Avalanche Forecast

Issued: Feb 21st, 2016 7:45AM

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

pmarshall, Avalanche Canada

Purcells.

There is potential to trigger very large and dangerous avalanches, especially in the Northern part of the Purcells. Conservative terrain choices are essential.

Summary

Confidence

Moderate

Weather Forecast

Monday: Cloudy with flurries in the morning and sunny breaks in the afternoon. The freezing level is around 1500 m and ridge winds are light from the NW. Tuesday: Mainly sunny. The freezing level is around 1500 m and ridge winds are light from the W-SW. Wednesday: Mainly sunny. The freezing level is around 1600 m and ridge winds are light to moderate from the W-SW.

Avalanche Summary

On Saturday one person was killed and another was hospitalized in a large avalanche in the Quartz Creek area west of Golden. This size 3 snowmobile-triggered slab avalanche occurred on a S-SW aspect in the alpine and is suspected to have released on the Feb. 12 interface. Explosive control in other areas produced a few slabs, cornice falls, and loose dry slides up to size 2. Natural wind slab avalanches up to size 2.0 were reported on Friday, as well as skier accidental storm slabs to size 1.5.

Snowpack Summary

20-30 cm of snow in the past few days has added to the recent storm slab above the buried crust buried about 40-60 cm below the surface. This melt freeze crust likely exists in most places except for in high elevation shaded terrain. In general there seems to be a reasonable bond between the crust and the overlying snow. I'd still keep an eye on this interface as it has become reactive on some features. Periods of strong solar radiation may increase the likelihood of triggering the storm slab. In isolated areas there may be a weak layer of surface hoar at the storm snow/crust interface that is touchy to human triggers and may result in wide propagations. The early January surface hoar/ facet layer is typically down 70-120 cm. Avalanche activity at this interface has tapered-off over the past week, but I'd be reluctant to trust this potentially destructive layer just yet. In general, the lower snowpack is well settled and strong, apart from some thin snowpack areas where basal facets exist.

Problems

Persistent Slabs

It may be possible to trigger weaknesses within the recent storm snow or at the crust interface at the bottom. be particularly cautious in wind-loaded and cross-loaded terrain near ridge crests.

Be cautious as you transition into wind affected terrain.>Choose conservative lines and watch for clues of instability.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 4

Deep Persistent Slabs

The early January surface hoar may continue to be triggered by large loads like storm snow avalanches in motion, or light loads in shallow or weak spots on large terrain features. This problem is more likely in the north of the region near Golden.

Avoid convexities or areas with a thin or variable snowpack.>Avoid thin, rocky or sparsely-treed slopes.>Be cautious around open slopes and convex rolls at and below treeline where buried surface hoar may be preserved. Big alpine features are also suspect.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

3 - 6

Cornices

Natural cornice falls may trigger storm slab avalanches on the slopes below. Periods of strong solar radiation may increase the likelihood of natural cornice falls.

Extra caution needed around cornices with current conditions.>Cornices become weak with daytime heating. >

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 4

Valid until: Feb 22nd, 2016 2:00PM