Avalanche Canada dsaly, Avalanche Canada

Sea to Sky Avalanche Forecast

Feb 17th, 2020 5:00PM

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

Sun and warm temperatures have helped the snowpack settle and bond. Keep an eye on sunny slopes warming through the day, move to more shaded terrain and avoid overhead hazards if the surface snow becomes moist or wet.

Summary

Confidence

Moderate - Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack.

Weather Forecast

MONDAY NIGHT: Partly cloudy. Alpine low temperature -8 C. Northwest wind 10-15 km/hr. Freezing level valley bottom.

TUESDAY: Sunny. Alpine high temperature -3 C. Northeast wind 10-20 km/hr. Freezing level 1000 m.

WEDNESDAY: Sunny with clouds. Alpine high temperature +2 C. South wind 15-20 km/hr. Freezing level 1500 m.

THURSDAY: Mix of sun and cloud. Alpine high temperature -1 C. Southwest wind 10-20 km/hr. Freezing level 1200 m.

Avalanche Summary

Skiers triggered loose, dry sluffing in steep terrain on Sunday. On Saturday, small size (1-1.5) wind slab avalanches were triggered by skiers and explosives in the alpine and treeline. On Friday fast moving storm slabs with crowns averaging 20 cm in depth were quite sensitive to human triggers and explosive control work to size 1.5. Control work also produced cornice failures to size 2.5.

A very large (size 3.5) avalanche was observed on February 9th near Whistler on a steep north face at 2400 m. It is suspected to have failed on a layer of facets on a crust from late November. This very large event demonstrates the ongoing need for caution in aggressive alpine terrain.

Snowpack Summary

10-30 cm recent snow has be redistributed by southwesterly winds and a crust has formed on solar aspects. The new snow overlies wind affected snow in the alpine, a crust on solar aspects, and lower density snow or spotty surface hoar in sheltered terrain. 

A rain crust sits 30-50 cm below the surface at elevations below 2000 m. The bond at this interface appears to be reasonably strong and the mid pack well settled. 

While weak faceted grains and crusts near the base of the snowpack have mostly not been a problem recently, a very large avalanche was observed on this layer on Feb 9. The problem appears isolated to very aggressive alpine terrain and is likely more prevalent in inland parts of the region.

Terrain and Travel

  • Be alert to conditions that change with elevation and wind exposure.
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet

Problems

Wind Slabs

An icon showing Wind Slabs

Likelihood

Unlikely-Possible

Expected Size

1 - 1.5

Watch for pockets of wind slab around ridges and steep rolls at upper elevations. Keep an eye on cornices and overhead hazards, especially as the sun bakes the surface snow.

Aspects:

North, North East, East, South East, North West.

Elevations:

Alpine.

Loose Wet

An icon showing Loose Wet

Likelihood

Possible

Expected Size

1 - 1.5

South-facing aspects are expected to warm with strong input from the sun. Be mindful of cornices and sun impacting hazards above you.

Aspects:

South East, South, South West.

Elevations:

All elevations.

Valid until: Feb 18th, 2020 5:00PM