Avalanche Forecast

Issued: Mar 14th, 2017 4:11PM

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

mgrist, Avalanche Canada

Purcells.

Warming and heavy snow will overload the snowpack and drive the danger to HIGH. Surprising avalanche results may occur given our current snowpack. Conservative terrain use is essential this week and avoid overhead hazard.

Summary

Confidence

Moderate - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

Warm temperatures and high freezing levels continue with moderate winds and heavy snow on Wednesday.WEDNESDAY: We'll see 15-25cm of fresh snow (above 1700m), accompanied by moderate south winds. Freezing levels near 1900m.THURSDAY: Sunny breaks with flurries (5-10cm) accompanied by moderate southwest winds. Freezing levels dropping to 1300m.FRIDAY: Cloudy with isolated flurries (up to 5cm) with light to moderate southwest winds. Freezing levels near 1200m.

Avalanche Summary

On Monday natural storm slabs to Size 2 were reported above 2400m on south and east aspects. 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.

Snowpack Summary

Around 20-50cm of fresh snow in the past several days has fallen with light to moderate southwest winds. These winds have formed touchy slabs at upper elevations with multiple weaknesses within and under this recent storm snow.Warming temperatures on Sunday into Monday has resulted in moist (read: heavy) surface snow up to 2000m in most areas, and some unstable snow below treeline.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 20-50 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 15th, 2017 2:00PM