Avalanche Forecast

Issued: Mar 18th, 2017 3:00PM

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

Avalanche Canada mgrist, Avalanche Canada

Rapid loading, warm temperatures and strong wind are a recipe for HIGH danger. Avoid avalanche terrain and stay well back from runout zones.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

We'll see lingering flurries on Sunday as it cools down significantly. Clearing Monday onwards.SUNDAY: Broken skies with isolated flurries / moderate to strong west wind / Alpine temperature -8 / Freezing level 800mMONDAY: Increasing cloud in the afternoon and some scattered flurries / Light east wind / Alpine temperature -6 / Freezing level 1200mTUESDAY: Isolated flurries / Light to moderate southwest wind / Freezing level 1500m

Avalanche Summary

On Friday skiers triggered a Size 1.5 wind slab quite low down on a slope - strong winds had transported snow farther than expected. On Thursday a Size 2.5 natural slab avalanche on a west aspect took out trees. The sun came out in force and cornices were failing. See here for this great MIN report.There was a widespread natural avalanche cycle to size 3 on all aspects and elevations from last Wednesday's storm in the areas south of Valemount. Expect the storm slabs to continue to be reactive at upper elevations, especially with more loading on Saturday.

Snowpack Summary

In the south of the region, heavy snow (25 cm in 10 hours) and strong winds (gusts over 60 Km/hr) started late Friday and continued through Saturday. Temperatures also warmed up significantly. The end result: Widespread storm slabs and wind slabs at treeline and above with significant cornice growth as well. All this new snow 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. Approximately 100-140 cm below the surface you may find the mid-February persistent weakness. Professionals in the region have warned that the load above this layer has reached a critical amount, particularly where it presents as a crust.Deep persistent weaknesses in the lower third of the snowpack still have the potential to react to human triggers or smaller slab avalanches, especially with the warming temperatures and/or intense sunshine early next week. New snow totals in the north (Wells, Sugar Bowl) have been half to one-third of those in the south and avalanche danger is likely one step lower.

Problems

Storm Slabs

An icon showing Storm Slabs
More warm storm snow on Saturday combined with moderate to strong southwest wind created a touchy storm slab problem. Avoid avalanche terrain and stay well back from runout zones.
Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.The new snow will require several days to settle and stabilize.If triggered, the storm slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 3

Persistent Slabs

An icon showing Persistent Slabs
Persistent weakness layered throughout the snowpack create the potential for very large step-down avalanches. The risk of triggering a deeper weak layer will be heightened while overlying storm slabs remain sensitive to human triggering.
Be aware of the potential for large, deep avalanches due to the presence of buried weak layers.Avoid or use extreme caution around thin snowpack areas.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2 - 4

Valid until: Mar 19th, 2017 2:00PM

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