Avalanche Forecast

Issued: Apr 7th, 2018 3:58PM

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

mconlan, Avalanche Canada

South Coast Inland.

Recent snowfall with strong winds has produced new slabs at higher elevations. Expect avalanche activity to increase on southerly aspects if the sun comes out.

Summary

Confidence

Moderate -

Weather Forecast

SUNDAY: A mix of sun and cloud, light westerly winds, alpine temperature -3 C, freezing level 1500 m.MONDAY: A mix of sun and cloud, light southwesterly winds, alpine temperature -3 C, freezing level 1600 m rising to 2000 m by late afternoon.TUESDAY: Mostly cloudy with afternoon precipitation, accumulation 5 mm, alpine temperature 0 C, freezing level 2600 m dropping to 2000 m.

Avalanche Summary

On Friday, a large (size 2.5) persistent slab avalanche was triggered by a cornice on a northeast aspect around 1900 to 2200 m. The slab likely released on the weak layer described in the Snowpack Summary. Other similar large avalanches were observed, as described in this MIN post.Small to large (size 1 to 2) wind slabs were also reactive to skiers and large loads, generally failing in alpine terrain in immediate lee terrain features. Loose wet avalanches were observed across the region on all aspects to size 1.5.

Snowpack Summary

Around 20 cm of snow and strong southwesterly winds created new slabs at higher elevations. This snow overlies various old surfaces including previous storm snow, melt freeze crusts on sunny aspects, and old wind slabs. On ridges, cornices are reported to be large and fragile. At lower elevations, precipitation fell as rain and created wet snow conditions.A weak layer consisting of surface hoar, facets, or a sun crust from late March is now buried about 40 to 70 cm. This layer is spotty in its distribution. It is mostly likely to be problematic on shady aspects between 1900 m and 2250 m.The mid and lower snowpack are strong and well-settled.

Problems

Storm Slabs

Recent snowfall has formed new slabs. Expect thicker slabs in lee features due to strong southerly winds. Slab or loose wet avalanches could release naturally when the sun is out or the air temperature warms.

Avoid sun-exposed slopes when the solar radiation is strong, especially if snow is moist or wet.Observe for the bond of new snow with the old surface before committing into avalanche terrain.Use ridges or ribs to avoid pockets of wind-loaded snow.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Persistent Slabs

A weak layer buried 40 to 70 cm is still surprising people and producing large and destructive avalanches. Be particularly cautious around upper treeline and alpine terrain on shady aspects, where this layer is most likely to be a problem.

Be aware of the potential for wide propagation due to the presence of buried weak layers.Avoid steep terrain or areas with a thin or variable snowpack.Pay attention to overhead hazards like cornices, which could trigger persistent slabs.

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 3

Cornices

Cornices are very large and fragile. Give them a large berth when on ridges and avoid travelling underneath them, as they can trigger large avalanches on slopes below.

Pay attention to overhead hazards like cornices, which could trigger persistent slabs.Stay well back from cornices.

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

2 - 3

Valid until: Apr 8th, 2018 2:00PM