Avalanche Forecast

Issued: Mar 14th, 2017 4:19PM

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

rbuhler, Avalanche Canada

Sea To Sky.

On Wednesday, touchy storm slabs are expected in the high alpine. Extra caution is also required on all sun exposed slopes if the sun comes out in full force.

Summary

Confidence

Moderate -

Weather Forecast

Wednesday is expected to be mainly dry with a chance of sunny breaks and moderate alpine wind from the southwest. Freezing levels are forecast to drop to around 1000 m Tuesday overnight and reach around 1500 m in the afternoon. The next pulse of precipitation is expected to arrive Wednesday overnight or Thursday morning and 20-30 mm is currently forecast between Thursday morning and Friday morning. Alpine wind is expected to be moderate from the southwest on Thursday with freezing levels around 1000 m. Friday is currently forecast to be mainly dry with the next storm system arriving Friday overnight or Saturday morning.

Avalanche Summary

On Monday, natural storm slab avalanches up to size 1.5 were observed west of Bralone. In the Whistler area, explosives were triggering storm slabs up to size 2 and a skier triggered a size 1.5 storm slab on a north aspect at 2100 m elevation. Most of this storm slab activity had slab thickness of 20-30 cm but one was 80 cm thick in a wind loaded pocket. A natural cornice release was also reported on a northeast aspect at 2300 m. On Sunday, two explosives triggered size 2 storm slab avalanches were reported. One of these featured a 60 cm crown fracture and is suspected to have stepped down to a deeper weak layer, quite possibly the mid-February interface.On Wednesday, stability is generally expected to improve as temperatures drop. However, if the sun comes out, it can quickly destabilize the snowpack on sun exposed slopes. In the high alpine, the recent storm snow is expected to remain touchy, especially in wind loaded terrain.

Snowpack Summary

On Tuesday, freezing levels reached at least 2200 m and rain was reported to at least 2000 m. As temperatures drop on Wednesday, a new surface crust is expected to be widespread. The mid-February crust/facet layer is now typically down 80-120 cm. In wind loaded terrain, it may as deep as 200 cm. With 5-20 cm of faceted, sugary snow above it, this mid-February crust layer continues to produce easy, sudden results in snowpack tests and remains an ongoing concern. Below the crust layer, the mid and lower snowpack are well settled and strong.

Problems

Storm Slabs

In the high alpine, recent storm snow is expected to be touchy on Wednesday, especially in wind loaded terrain. Extra caution is also needed around cornices right now.

Avoid freshly wind loaded features.Be alert to conditions that change with elevation.Give cornices a wide berth when travelling on or below ridges.

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Likely

Expected Size

1 - 2

Persistent Slabs

A weak layer down around 1 metre is creating a low probability/high consequence scenario. It may still be possible to directly trigger this layer in isolated areas or a small avalanche or cornice fall could step down to it.

Choose conservative lines in supported terrain.If triggered, storm slabs may step down to deeper layers resulting in very large avalanches.Be aware of the potential for large avalanches due to the presence of deeply buried weak layers.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2 - 4

Loose Wet

If the sun comes out in full force, expect sluffing from steep sun exposed slopes. Cornices will also become weak with prolonged sun exposure.

Be cautious of sluffing in steep terrain.Minimize exposure to steep, sun exposed slopes when the solar radiation is strong.Give cornices a wide berth when travelling on or below ridges.

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

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 2

Valid until: Mar 15th, 2017 2:00PM