Avalanche Forecast

Issued: Mar 19th, 2017 4:05PM

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.

We've weathered the storm but we're not out of the woods yet. There's a great blog post on critical factors to watch out for this spring. Click here for details.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Clear and cool on Monday and then some clouds move in (with isolated flurries) for the rest of the forecast period.MONDAY: Sunny with increasing cloud in the afternoon / Light east wind / Alpine temperature -6 / Freezing level 1200mTUESDAY: Isolated flurries / Light to moderate southwest wind / Freezing level 1500mWEDNESDAY: Broken skies with isolated flurries / moderate south wind /Freezing level 1600m

Avalanche Summary

On Saturday morning a Size 2 storm slab (crown height 15-20cm) was remote-triggered on a bootpack path in the backcountry near Golden. Also on Saturday, a Size 4 natural avalanche was reported in the northern part of the region starting at 2700m on an east aspect and running 1400 metres to valley bottom, gouging to ground in some locations. The past few days warm and wet weather have seen a natural avalanche cycle to Size 4 from a variety of aspects and elevations. In the wake of Saturday's storm expect the likelihood of triggering an avalanche to remain elevated.

Snowpack Summary

Heavy snow (15-20 cm in 12 hours) and moderate southerly winds started late Friday and continued all through Saturday. Temperatures also warmed up significantly with rain up to 2100m. The end result: Widespread reactive storm slabs and wind slabs at treeline and above with significant cornice growth as well.This storm snow (totals of 40-70cm) sits on older windslabs (or soft slabs) at treeline and above. Below 1800m, the new snow sits on a melt-freeze crust from last week's warm storm, and reports so far are that the new snow is bonding well to the old crust.The persistent weakness buried late-February is now down 90-140cm, and is composed of weak facetted crystals on a thick rain crust as high as about 2000m and facets on sun crust on steep southerly aspects. This layer has produced easy-moderate 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 and mid-January (primarily in the northern Purcells). The november crust and basal facets are still reactive in shallow, rocky start zones.

Problems

Storm Slabs

Warm storm snow on Saturday combined with strong southwest wind created a touchy storm slab problem. The snowpack will need time to adjust to the new load - stick to low angled terrain (with no overhead hazard) and avoid sunny slopes on Monday.

If triggered the storm slabs may step down to deeper layers resulting in large avalanches.The new snow will require several days to settle and stabilize.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 3

Persistent Slabs

Various persistent weaknesses strewn throughout the snowpack create the potential for large step-down avalanches. Heavy loads such as a smaller storm/wind slab avalanche or a cornice fall increase the likelihood of triggering these layers.

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.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 4

Valid until: Mar 20th, 2017 2:00PM