Avalanche Forecast

Issued: Dec 18th, 2020 8:01AM

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

Percy Woods,

The AVALANCHE danger is increasing with the building storm slab overĀ  weak surface hoar. Make conservative terrain choices.

Summary

Weather Forecast

Flurries today with another 7cm of accumulation.

Alpine high of -6C with ridge winds SW moderate to strong.

Freezing level 1200m.

Tonight through Sunday upwards of 30cm storm snow accompanied by SW winds moderate gusting to extreme.

Snowpack Summary

Wind, warmth and continued snowfall have formed a sensitive storm slab at all elevations over the Dec 13 surface hoar layer. Weak layers of concern are Dec 13 surface hoar down 45cm+ and Dec 7 crust/surface hoar layer down 65cm+. The Nov 5 crust has been unreactive to stability tests.

Avalanche Summary

Numerous size 1-2 skier remote avalanches were triggered yesterday both in the west end of the park and the Asukan and Illecillewaet valleys. On Wednesday a skier went for a ride in a size 1.5 slide below treeline elevation. Numerous avalanches to size 3.5 were recorded in the highway corridor yesterday.

Confidence

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

Problems

Storm Slabs

An icon showing Storm Slabs

Storm slabs continue to build over the Dec 13 surface hoar layer. This layer, down 40cm+, was very sensitive to human and natural triggering yesterday. This layer is reactive at all three elevation bands.

  • Watch for whumpfing, hollow sounds, and shooting cracks.
  • Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1 - 3

Persistent Slabs

An icon showing Persistent Slabs

70cm+ sits on the Dec 7th weak interface of rain crust/ surface hoar. If triggered the storm slab has potential to step down to this interface triggering large avalanches.

  • Minimize overhead exposure during periods of heavy loading from new snow, wind.
  • If triggered the storm slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 3

Valid until: Dec 19th, 2020 8:00AM