Avalanche Forecast

Issued: Mar 19th, 2017 3:22PM

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.

Avalanche Canada mgrist, Avalanche Canada

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 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 from Saturday's storm.

Snowpack Summary

In the south of the region, heavy snow (25 cm in 10 hours) and strong south-west 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 storm snow (30- 60cm) 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 on Monday.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
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

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.
Avoid or use extreme caution around thin snowpack areas.Be aware of the potential for large, deep avalanches due to the presence of buried weak layers.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2 - 4

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