Avalanche Forecast

Issued: Apr 18th, 2013 10:54AM

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

Avalanche Canada jlammers, Avalanche Canada

Summary

Confidence

Fair - Forecast snowfall amounts are uncertain on Thursday

Weather Forecast

Thursday night and Friday: Moderate snowfall tapering to light on Friday (higher amounts are more likely in the South end of the region) / Moderate southwest winds becoming light on Friday / Freezing levels at about 1500mSaturday: Cloudy with isolated flurries / Moderate west winds / Freezing level at 1500mSunday: Ridging will develop resulting in clearing skies and rising freezing levels

Avalanche Summary

Numerous rider triggered and isolated remote/sympathetic events have been reported in high (2300-2700m) north and northeast facing slopes up to size 2.5, all associated with preserved surface hoar. Much of the reported activity on buried surface hoar seems to be occurring in the north of the region in the Duffey Lake/ Birkenhead areas, through the Hurley and up towards Bralorne/Goldbridge.

Snowpack Summary

North and Northeast aspects above 2000m continue to hold dry snow; otherwise, the surface condition is crusts. The carrying strength of the crusts varies depending on aspect and elevation as well as proximity to rocks, etc.... Generally speaking, the crusts have been going moist in the afternoon and then refreezing at night in all but the lowest terrain. Recent storm snow has settled into a cohesive slab between 30-60cm deep. At the interface of this storm snow lies the April 05 layers. On solar aspects, the layer is a strong melt-freeze crust, with some faceting observed above and below. Reactivity on this layer has been inconsistent, with occasional sudden results and some whumphing. On North and Northeast aspects above about 2300m, this interface may be preserved surface hoar (up to 15mm). Where the surface hoar is present we have reports of sudden results in stability tests and have seen rider triggered, sympathetic and remote events up to size 2.5. Professional operators express consistent concern for triggering this layer.Cornices are huge and will continue to grow with the forecasted precipitation.

Problems

Persistent Slabs

An icon showing Persistent Slabs
The April 05 interface lingers as a persistent problem. Surface hoar on N/NE aspects above about 2300m and (to a lesser extent) facets on a crust on solar aspects.
Be aware of the potential for large avalanches due to the presence of buried surface hoar.>Be alert to conditions that change with elevation.>Carefully evaluate big terrain features by digging and testing on adjacent, safe slopes.>

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

Elevations: Alpine.

Likelihood

Possible - Likely

Expected Size

1 - 5

Wind Slabs

An icon showing Wind Slabs
New softslabs will form in lee features with the forecast new snow.
Stay off recent wind loaded areas until the slope has had a chance to stabilize.>

Aspects: North, North East, East.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 4

Cornices

An icon showing Cornices
New snow and wind will add mass to existing cornices. Cornices can act as a large trigger to deeper weaknesses.
Stay well back from cornices.>Pay attention to overhead hazards like cornices.>

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 6

Valid until: Apr 19th, 2013 2:00PM