Avalanche Forecast

Issued: Feb 18th, 2016 8:45AM

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

triley, Avalanche Canada

Purcells.

There is a great deal of variability across the region at this time. Several more pulses of snow and wind are expected over the next few days.

Summary

Confidence

Moderate - Intensity of incoming weather systems is uncertain

Weather Forecast

Light snow (3-5 cm) and moderate to strong westerly winds overnight with the freezing level dropping to valley bottoms. Light snow during the day Friday becoming moderate snow in the evening. Snow will be combined with moderate westerly winds and freezing levels rising up to 1400 metres. Some chance of sunny breaks during the day on Friday. Flurries or light snow during the day on Saturday with light winds and freezing levels climbing from valley bottoms up to 1400 metres. Mostly clear on Sunday with light winds and freezing levels climbing from valley bottoms up to 1400 metres.

Avalanche Summary

On Wednesday there were reports of natural cornice falls up to size 2.5, and explosives control released slab avalanches up to size 2.5. Most of the slab avalanches were in the alpine on east aspects. On Tuesday we had reports of explosives controlled slab avalanches up to size 3.0 in the west central part of the region, and thin new windslabs in the north that were skier controlled, as well as a size 2.5 deep persistent slab avalanche was reported that probably released on Monday on a west aspect in the alpine. On Monday we had reports of natural wind slab avalanches up to size 2.0, and one wind slab in the alpine that stepped down to a persistent week layer on an east aspect resulting in a size 3.0 avalanche.

Snowpack Summary

There has been 15-30 cm of new snow in the past few days that has added to the recent storm slab above the buried crust. About 25-50 cm below the surface, you'll likely find a melt freeze crust which 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. 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

Storm Slabs

Storm slabs are deep and continue to load with each pulse of stormy weather. Buried surface hoar at the storm snow/crust interface may result in wide propagations and large avalanches.

Minimize exposure during periods of heavy loading from new snow, wind.>Be cautious as you transition into wind affected terrain.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 3

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.

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.>Avoid thin, rocky or sparsely-treed slopes.>Avoid convexities or areas with a thin or variable snowpack.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

3 - 5

Cornices

Cornices may be large and fragile. Cornice growth continues with each pulse of new snow and wind. Natural cornice falls may trigger storm slab avalanches on the slopes below.

Do not travel on slopes that are exposed to cornices overhead.>Extra caution needed around cornices with current conditions.>

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

Elevations: Alpine.

Likelihood

Likely - Very Likely

Expected Size

1 - 4

Valid until: Feb 19th, 2016 2:00PM