Avalanche Canada ghelgeson, Avalanche Canada

Sea to Sky Avalanche Forecast

Feb 15th, 2020 4:00PM

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

Potentially touchy wind slabs in exposed terrain at and above treeline are the primary concern, but we can't take our eyes off the monster cornices either. There is potential for the strengthening February sun to make them more prone to failure.

Summary

Confidence

Moderate - Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack. Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack.

Weather Forecast

We’re moving into a dryer period that is expected to be with us for the foreseeable future. Freezing levels look very reasonable for the middle of February and there is a lot of sun in the forecast Sunday through Wednesday.

SATURDAY NIGHT: Freezing level around 1000 m, light to moderate west/northwest wind, trace of snow possible.

SUNDAY: Broken cloud cover, freezing level around 900 m, light to moderate west/northwest wind, trace of snow possible.

MONDAY: A few clouds, freezing level around 800 m, light variable wind, no significant precipitation expected.

TUESDAY: Clear skies, freezing level rising to about 1300 m, light variable wind, no significant precipitation expected.

Avalanche Summary

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.

On Thursday, large cornices were reactive to explosives and skiers, and one failed naturally. Explosives triggered wind slab avalanches to size 1.5, which failed over a crust.

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 to 20 cm of snow fell Friday Night into Saturday accompanied by wind out of the south which is expected to further wind slab development in lee features at alpine and upper treeline elevations. The new snow overlies a variable surface of harder wind slabs, a sun crust on solar aspects, and settled snow 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.

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

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • Be alert to conditions that change with elevation and wind exposure.

Problems

Wind Slabs

An icon showing Wind Slabs

Likelihood

Possible-Likely

Expected Size

1 - 2

By Sunday morning the total amount of storm snow from the last few days should be between 10 and 40 cm. This snow has combined with moderate to strong winds which have recently been out of both the northwest and southwest. Wind slabs can be found on a variety of aspects in exposed alpine and treeline terrain. Where wind slabs sit over a crust, they may be more sensitive to triggering.

Aspects:

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

Elevations:

Alpine, Treeline.

Valid until: Feb 16th, 2020 5:00PM