Avalanche Forecast

Issued: Mar 12th, 2017 6:02PM

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

mgrist, Avalanche Canada

Purcells.

Snow, wind and warming are a recipe for elevated danger. Storm and wind slabs will be touchy at treeline and above. Avoid overhead hazard: Conservative terrain use is essential this week!

Summary

Confidence

Moderate - Intensity of incoming weather systems is uncertain

Weather Forecast

We'll have light snowfall amounts through to Monday afternoon, and then it starts to warm up.MONDAY: Cloudy with another 5-10cm by late afternoon accompanied by moderate SW winds and freezing levels rising as high as 1500m.TUESDAY: Scattered flurries (3-5cm) with moderate southerly winds. Freezing levels remain near 1600m.WEDNESDAY: Cloudy with another 5-15cm of fresh snow by late afternoon and continued light flurries throughout the day accompanied by light to moderate SW winds. Alpine temperatures hovering around -3 C.

Avalanche Summary

On Sunday afternoon a rider-triggered Size 2.5 persistent slab avalanche was reported near Golden. Average slab depth was 50cm on a steep north facing aspect near 2300m.Several storm and persistent slab avalanches to Size 3 were also reported on Sunday - most activity was above 2300m on a variety of aspects. 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 an alpine wind loaded feature. See here for this informative MIN post.

Snowpack Summary

Around 20-40cm of fresh snow in the past three days has added to the 40-80cm of settled recent storm snow. Southerly winds have formed touchy slabs at upper elevations with multiple weaknesses within and under this recent storm snow.All this snow is bonding poorly to weak faceted snow and small surface hoar on sheltered shady slopes, and/or a thin crust on southerly aspects.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 is expected to increase the likelihood of these large 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

Unlikely - Possible

Expected Size

2 - 4

Valid until: Mar 13th, 2017 2:00PM