Avalanche Forecast

Issued: Mar 12th, 2017 5:46PM

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

Avalanche Canada cgarritty, Avalanche Canada

Steadily warming temperatures are increasing concern for persistent slab avalanches. A smaller storm slab release could be the perfect trigger.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain on Monday

Weather Forecast

Monday: Scattered flurries bringing up to 5 cm of new snow, transitioning to rain below 1500 metres in the afternoon. Moderate to strong southwest winds. Freezing level rising to 1900 metres over the day. Alpine temperatures of -1 to 0. Tuesday: Isolated alpine flurries, rain showers below around 1600 metres, intensifying overnight. Moderate south winds. Freezing rising to 2000 metres over the day with alpine temperatures of 0 to +1. Wednesday: Continuing alpine flurries and rain showers below 1500 metres. Strong southwest winds. Freezing level dropping to 1500 metres over the day with alpine temperatures of 0 to -1.

Avalanche Summary

Reports from Saturday include one observation of a Size 1 persistent slab releasing with a ski cut on an east aspect over the mid February weak layer in the Hurley area. Several more Size 1 slabs were reported releasing on northerly aspects in the north of the region under a range of triggers, including natural and remote.Reports from Friday showed several wind slabs failing naturally and with remote triggers from Size 1-2.5 in the north of the region. The largest of these initiated on a southeast aspect at 2100 metres, is suspected to have failed on the late February weak layer, and featured a crown fracture depth of 80-120 cm.Reports from Thursday included one explosives triggered Size 3 avalanche in the Duffey Lake area that began as a shallow surface slab before stepping down to one of our February weak layers. Looking forward, recent persistent slab avalanche activity supports ongoing concern for large avalanches releasing on our February weak layers, especially in the north of the region. While natural avalanches on these layers may become unlikely, evidence suggests the possibility for a rider to directly trigger a persistent slab or for a smaller avalanche to 'step down'.

Snowpack Summary

A week of stormy weather has brought 80-120 cm of recent snow to the north of the region and roughly 150 cm to the south. Recent south to southwest winds have redistributed much of this snow in wind-exposed terrain, forming touchy wind and storm slabs. The above mentioned storm snow overlies the mid-February and late-February interfaces, which may be close together in the snowpack. The late-February interface consists of wind affected surfaces in exposed terrain, sun crust on steep solar aspects, and facets and surface hoar in sheltered areas. The mid-February interface consists of a thick rain crust which extends to at least treeline, a sun crust on steep solar aspects, and in many places, a layer of facets overlying the crust. Recent snowpack observations and avalanche activity suggest the late-February layer is most reactive in the north of region while the mid-February layer may be becoming unreactive in the south of the region. Below these layers, the mid and lower snowpack are generally well settled and strong.

Problems

Storm Slabs

An icon showing Storm Slabs
More light snowfall will combine with strong overnight winds to contribute to our storm slab problem. Expect the problem to become increasingly focused to wind affected areas and lee terrain. Warm temperatures are also expected to promote reactivity.
Avoid areas where the new snow feels stiff or slabby.Use caution in lee areas in the alpine and treeline. Recent snow and wind have formed touchy slabs.Be careful around wind loaded pockets, especially near ridge crests and roll-overs.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 2

Persistent Slabs

An icon showing Persistent Slabs
Recent large avalanches have run on a weak layer buried up to a metre below the surface in the north of the region. This type of feedback can't be ignored. Warming temperatures and incremental loading increase the potential for deep releases.
Be aware of the potential for large avalanches due to the presence of deeply buried weak layers.Use conservative route selection, choose moderate angled and supported terrain with low consequence.If triggered, storm or wind slabs may step down to deeper layers resulting in very large avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 4

Valid until: Mar 13th, 2017 2:00PM

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