Avalanche Forecast

Issued: Apr 18th, 2017 4:48PM

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

mgrist, Avalanche Canada

Sea To Sky.

Wind slabs and cornices are the main concerns right now. Carefully assess terrain before committing to bigger lines.

Summary

Confidence

Moderate - Intensity of incoming weather systems is uncertain

Weather Forecast

We're looking at unsettled and variably wet spring weather through Thursday, with clearing and fine weather for Friday.WEDNESDAY: More wet snow (5-15cm) above 1400m and the potential for intense squalls (and thunderstorms). Winds moderate southerly.THURSDAY: Isolated flurries (5-10cm) with wet snow above 1500m. Winds light southwesterly.FRIDAY: Sunny with cloudy periods. Freezing level rising to 2300m. High temperatures to +6 Celsius. Winds light southerly.NOTE: The convective flurries which are common during this time of year can result in widely varying snowfall amounts throughout a region. These spring squalls routinely drop 20+ cm of snow in one valley while the adjacent drainage remains dry. For this reason, the distribution of avalanche problems associated with new snow, such as wind slabs, can vary greatly within a region.

Avalanche Summary

On Tuesday we had reports of easily triggered soft slabs to Size 2 in the storm snow near Whistler. On Monday we had preliminary reports of an avalanche involvement in the Tantalus range near 2000m, aspect not known. All in the party got out safely.On Sunday, skiers triggered a Size 1.5 slab avalanche in a northwest facing couloir in the alpine near Whistler. See here for their MIN report. On Saturday, skiers triggered a Size 1.5 wind slab on the Spearhead traverse near Fissile, on a southwest aspect. See here for more details.

Snowpack Summary

On Monday into Tuesday we've had 10-15cm of fresh snow above 1400m. Southerly winds have created pockets of reactive wind slab (20-50cm thick) in the alpine and exposed features at treeline. Wind slabs have surprised skiers throughout the long weekend (see Avalanche Summary above). Warm temperatures on Sunday (+5 at treeline) and solar radiation resulted in a melt-freeze crust on south aspects at all elevations. The new snow is not expected to bond well to this crust and storm slabs may be more reactive on south aspects. Cornices remain large in some areas and could trigger large avalanches when they fail. The fatal accident near Lions Bay a week ago illustrates the danger of cornices breaking off, and the large avalanches they can trigger.

Problems

Wind Slabs

Wind slabs have formed in the alpine and also near exposed treeline features.

Use ridges or ribs to avoid pockets of wind loaded snow.Be cautious as you transition into wind affected terrain.

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Cornices

Where they exist, cornices pose a significant hazard and should be avoided.

Extra caution needed around cornices with current conditions.Give cornices a wide berth when travelling on or below ridges.Falling cornices can trigger large avalanches.

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 3

Loose Wet

Loose wet avalanches are more likely at lower elevations where the snowpack may be isothermal and precipitation falls as rain. Even small slides can have serious consequences.

Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Apr 19th, 2017 2:00PM