Avalanche Forecast

Issued: Mar 10th, 2017 4:11PM

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

cam_c, Avalanche Canada

Purcells.

Snow, wind, warming and sun-exposure will keep storm slabs touchy, and coupled with the potential for cornice triggers, the likelihood of massive deep persistent slabs is expected to increase.

Summary

Confidence

Moderate - Freezing levels are uncertain on Monday

Weather Forecast

SATURDAY: A mix of sun and cloud with localized periods of intense sun-exposure and isolated light flurries. Increasing cloud with light snow starting in the afternoon. Light southerly winds becoming moderate westerlies. Freezing levels rising as high as 1500m for southern areas, but remaining near valley bottoms in the north.SUNDAY: Mainly cloudy with 5-10cm of fresh snow by the morning, moderate westerly winds and freezing levels again rising to 1500m for southern areas, but remaining near valley bottoms in the north. MONDAY: A mix of sun and cloud with isolated light flurries, light to moderate southwesterly winds and freezing levels rising above 2000m in the afternoon.

Avalanche Summary

Reports from Thursday include two 50-150cm thick Size 2-2.5 skier remote triggered deep persistent slab avalanches, failing on facets and depth hoar above the November crust with impressive propagation across alpine wind loaded feature. Subsequent explosives control produced another 40-200cm thick Size 2.5 deep persistent slab avalanche with 5m deep deposit. Elsewhere, skiers remotely triggered a 50cm thick Size 3 wind slab avalanche and extensive explosives control produced slab avalanches up to Size 3 with large full depth full path avalanches in thin snowpack areas.

Snowpack Summary

Around 15-20cm of fresh snow has added to the 40-80cm of settled recent storm snow is bonding poorly to weak faceted snow and small surface hoar on sheltered shady slopes, and/or a thin crust on southerly aspects. Southerly winds have formed touchy slabs at all elevations with multiple weaknesses within and under this recent storm snow. The persistent weakness buried mid-February is lurking down 70-120 cm and composed of a thick rain crust as high as about 2000 m, sun crusts on steep southerly aspects, and spotty surface hoar on shaded aspects. This layer has produced easy results in recent snowpack tests and has proven especially reactive on steep southerly aspects. Several deeper persistent weaknesses also remain a concern, including surface hoar buried early-February (around a metre deep), and mid-January (well over a metre deep primarily in the northern Purcells). The november crust and basal facets are still sensitive in shallow, rocky start zones.

Problems

Storm Slabs

Weaknesses within and under the 40-100 cm of recent storm snow are susceptible to human triggering. These storm slabs are particularly deep and touchy on slopes loaded by southerly winds.

Be increasingly cautious as you transition into wind affected terrain.Be alert to conditions that change with elevation.If triggered, storm slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

2 - 3

Persistent Slabs

Various persistent weaknesses strewn throughout the snowpack create the potential for large step-down avalanches. Warming and sun-exposure is expected increase the likelihood of these massive avalanches, especially with cornice-fall triggers.

Be aware of the potential for large avalanches due to the presence of deeply buried weak layers.Avoid steep convexities or areas with a thin or variable snowpack.Be aware of overhead hazards and avoid lingering in runout zones.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 4

Valid until: Mar 11th, 2017 2:00PM