Avalanche Forecast

Issued: Mar 21st, 2017 3:11PM

The alpine rating is considerable, the treeline rating is moderate, and the below treeline rating is low. Known problems include Wind Slabs and Persistent Slabs.

shorton, Avalanche Canada

Northwest Coastal.

Wind slabs are growing while a deeper weakness continues to produce large avalanches. Evaluate the terrain and snowpack carefully before committing to steeper terrain.

Summary

Confidence

High -

Weather Forecast

WENDESDAY: Flurries starting overnight with 5-10 cm of new snow, strong southwest winds, alpine temperatures around -3 C. THURSDAY: Another 5-10 cm, strong southwest winds, alpine temperatures around -7 C.FRIDAY: Yet another 5-10 cm, sustained strong south winds, alpine temperatures around -4 C.

Avalanche Summary

Reports from Monday indicate the persistent slab problem is alive and well throughout the region. Reports include two size 3 natural avalanches north of Terrace, another size 3 avalanche that was remotely triggered from flat terrain by a snowmobiler north of Stewart, and a few smaller size 1.5-2 persistent slabs also likely triggered by humans. Most of these avalanches occurred on northerly aspects above treeline. One of the large naturals was likely triggered by solar radiation on a south aspect, while the other one by a cornice fall on a northeast aspect. In addition to the ongoing persistent slab problem, the incoming weather pattern is looking to continually build fresh wind slabs.

Snowpack Summary

Expect fresh wind slabs to form in the lee of exposed terrain as unsettled weather brings small amounts of new snow and strong southwest winds. Storm snow from last week is continuing to settle and get redistributed by predominately southerly winds. It may be reactive above a touchy 40 cm deep rain crust. At treeline and above, recent loading has stressed a 1 m deep weak interface composed of facets, crust, and surface hoar from late February. Recent reports suggest this layer is still reactive throughout the region, especially in the north. A non-supportive surface crust has formed over moist or wet snow at 1100 m and below.

Problems

Wind Slabs

A steady pulse of unsettled weather will build fresh wind slabs in the lee of exposed terrain. Be aware that recent winds have also built touchy cornices.

If triggered the wind slabs may step down to deeper layers resulting in large avalanches.Be careful with wind loaded pockets, especially near ridge crests and roll-overs.Be aware of especially touchy conditions where slabs overlie a rain crust

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Persistent Slabs

A persistent weak layer from late February is buried about a metre deep is still reactive. Potential still exists for a rider to directly trigger this layer or for a smaller wind slab or cornice to act as a trigger.

Use conservative route selection, choose moderate angled and supported terrain with low consequence.Avoid steep convexities or areas with a thin or variable snowpack.Be aware of the potential for large avalanches due to deeply buried weak layers.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 3

Valid until: Mar 22nd, 2017 2:00PM