Avalanche Forecast

Issued: Nov 19th, 2015 8:18AM

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

danyelle magnan, Parks Canada

Glacier.

Our early season snowpack is complex, with surface hoar layers, crusts, and pockets of basal facets. It was also just hammered with a dump of snow. Remember that it needs time to adjust to the new load as the sun lures you over the next few days.

Summary

Weather Forecast

An arctic high is moving over us, bringing dry cold weather. We may see a few flurries today and winds should shift to the NW at ridgetop and may reverse load slopes. Friday looks clear and cold, expect temps to drop to the low teens. Saturday we may see a mild inversion as temps start to rise back to around -5'C.

Snowpack Summary

~1m of storm snow is settling into a slab. Strong S-SW winds at treeline and above continue to load lee features, forming deep loaded pockets. Surface hoar layers down ~1m (Nov11) and 1.5m (Nov5) are still a concern. Weak facetted snow exists on high elevation N/NE aspects.

Avalanche Summary

Yesterday, there were several size 2-2.5 slab avalanches, likely triggered by wind-loading. Good visibility after the avalanche cycle from earlier this week showed that many avalanches were propagating widely, likely on the Nov 11 surface hoar. Some were also stepping down to deeper layers, including the Nov 5 surface hoar and the basal facets.

Confidence

Due to the number of field observations

Problems

Storm Slabs

A dump of ~100cm of snow early this week is settling into a slab. Strong SW winds have loaded lee features creating even deeper pockets, and continue to trigger natural avalanches. The snowpack still needs time to adjust to the rapid loading.

If triggered the storm/wind slabs may step down to deeper layers resulting in large avalanches.Avoid freshly wind loaded features.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 3

Loose Dry

In areas where the snow hasn't been wind-affected there is still lots of loose new snow. On steep slopes expect sluffing and be especially cautious around terrain traps like gullies, or over cliffs.

Be cautious of sluffing in steep terrain.Sluffs may trigger deeper instabilities.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Deep Persistent Slabs

On northerly alpine slopes, snow from early Sept was preserved and facetted forming a basal weakness. During the storm this week avalanches occurred on this layer. This layer was also responsible for a skier triggered size 3.5 avalanche 10 days ago.

If triggered the storm slabs may step down to deeper layers resulting in large avalanches.Avoid shallow snowpack areas where triggering is more likely.

Aspects: North, North East, East, South East.

Elevations: Alpine.

Likelihood

Possible

Expected Size

3 - 4

Valid until: Nov 20th, 2015 8:00AM