Avalanche Forecast

Issued: Apr 9th, 2018 4:43PM

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

mconlan, Avalanche Canada

South Coast Inland.

Expect changing weather on Tuesday: high freezing levels dropping over the day, intense rain switching to snow, and strong winds. Warming will weaken the snow and new snow will form fresh slabs. Be very cautious with these rapid changes.

Summary

Confidence

Moderate - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

TUESDAY: Cloudy with rain switching to snow, accumulation 10 to 20 cm, strong to extreme southwest winds, alpine temperature 0 C dropping to -5 C, freezing level 2600 m dropping to 1400 m over the day.WEDNESDAY: Mostly cloudy with snowfall, accumulation 5 to 10 cm, light to moderate southeast winds, alpine temperature -4 C, freezing level 1600 m.THURSDAY: A mix of sun and cloud, light west winds, alpine temperature -6 C, freezing level 1500 m.

Avalanche Summary

Loose and slab avalanches were observed on Sunday. Loose wet avalanches were observed on all aspects in steep terrain, being triggered naturally and by humans. Check out this MIN report from the north of the region, which discusses a large wind slab avalanche in alpine terrain that was triggered by a skier. They also noted reactivity of the recent storm snow around 1700 to 1800 m. Widespread whumphing was observed in a drainage in the north of the region, which was suspected to have been on the late-March weak layer described in the Snowpack Summary.

Snowpack Summary

Warm temperatures have moistened the snow surface on all aspects and at all elevations. At higher elevations, this overlies slabs formed from the weekend’s snow that fell with strong southwesterly winds. On Tuesday, new snow will fall with strong winds, forming new wind slabs in lee features. On ridges, cornices are reported to be large and fragile. At low elevations below treeline, recent rain has created moist or wet snow conditions.A weak layer consisting of surface hoar, facets, and/or a melt-freeze crust from late March is now buried about 50 to 100 cm. This layer is spotty in its distribution. It is mostly likely to be problematic on west, north, and east aspects between 1900 m and 2250 m.The mid and lower snowpack are well-settled and strong.

Problems

Wind Slabs

Wind slabs and loose wet avalanches will be reactive in the morning with warm and rainy weather. New slabs will form once the rain switches to snow. Strong southwest winds will mean that slabs will build quickly in lee features.

Avoid steep slopes when air temperatures are warm, it is raining, or the solar radiation is strong.Avoid overhead exposure, as avalanches may run full-path.Use ridges or ribs to avoid pockets of wind-loaded snow.

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

Elevations: All elevations.

Likelihood

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

Unlikely - Possible

Expected Size

2 - 3

Cornices

Cornices are very large and fragile. The morning's warm temperatures and rain will quickly deteriorate their stability. Give them a large berth while on ridges and avoid travelling underneath them, as they may trigger 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 10th, 2018 2:00PM