Avalanche Forecast

Issued: Feb 17th, 2016 8:44AM

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

triley, Avalanche Canada

Purcells.

Forecast new snow amounts and freezing levels are uncertain, due to weather models variability. Watch how high freezing levels climb, and avoid slopes that become moist or wet.

Summary

Confidence

Moderate - Freezing levels are uncertain

Weather Forecast

Light snow (3-5 cm) overnight with light southerly winds and freezing levels at about 1600 metres in the south and closer to 1000 metres in the north. Another 5-8 cm during the day on Thursday with increasing southwest winds and freezing levels up to about 1800 metres in the south. On Friday, expect flurries, light winds, and periods of broken skies. Freezing levels should rise up to about 1600 metres during the day and then fall to valley bottoms by Saturday morning. Scattered cloud with light southerly winds on Saturday, freezing level rising again to at least 1500 metres.

Avalanche Summary

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

Approximately 10 cm of new snow arrived by Tuesday morning. Moderate to strong westerly winds transported the new snow into wind slabs in the alpine and at treeline. The new snow will overlie wind slabs which formed over the past few days. About 15-40 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

Wind Slabs

Wind slabs may continue to be reactive where they are sitting on a buried crust that formed last week. Warm temperatures and high freezing levels may increase the likelihood of triggering.

Be cautious as you transition into wind affected terrain.>Travel on ridges to avoid freshly wind loaded features. >

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 3

Deep Persistent Slabs

The deeply buried persistent weak layer from early January continues to be a concern for human triggering. This problem appears to be more likely in the north of the region.

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 - 5

Loose Wet

Warm temperatures and forecast high freezing levels may result in loose wet avalanches in steep terrain at treeline and below.

Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 3

Valid until: Feb 18th, 2016 2:00PM