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Avalanche Forecast

Archived

Dec 16th, 2020–Dec 17th, 2020

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

South Columbia.

A pulse of flurries is forecasted to drop up to 20 cm. Expect to find a developing slab problem as wind impacts new flurries and older loose, dry snow. Choose conservative terrain and watch for signs of instability such as whumphing, cracking, and recent avalanches.

Confidence

Moderate - Uncertainty is due to the track & intensity of the incoming weather system.

Weather Forecast

WEDNESDAY NIGHT - Flurries, 15-20 cm / southwest wind, 20-40 km/h / alpine high temperature near -7 

THURSDAY - Isolated flurries, up to 10 cm / southwest wind, 20-40 km/h / alpine high temperature near -6

FRIDAY - Flurries, 10-20 cm / southwest wind, 20-50 km/h / alpine high temperature near -7

SATURDAY - Snow, 15-30 cm / southwest wind, 20-50 km/h / alpine high temperature near -4

Avalanche Summary

On Wednesday, a small (size 1) avalanche was triggered remotely by a vehicle traveling along an exposed ridgeline. Small windslabs gaining reactivity in the alpine was reported.

On Tuesday, small (size 1-1.5) storm slab avalanches were triggered by explosives and skier traffic on East, North, and West aspects above 2000 m; average depth 5-25 cm. 

Two surface hoar layers in the upper (30 cm) snowpack are providing poor bonding surfaces for new snow. With forecasted new snow and wind, storm slabs will become increasingly reactive, extending to all aspects and elevations.

Snowpack Summary

15-35 cm of new snow has fallen in the region since Wednesday morning. This new snow has likely buried a weak layer of surface hoar in many areas. This new snow combined with southwest winds is likely forming reactive slabs, especially at higher elevations. 

A weak layer that was buried about a week ago is now down 20-50 cm. This layer is variable and has been reported to exist as either a crust or surface hoar. This layer may react easily to human triggers.

Another crust that was buried in early November can be found near the base of the snowpack. There have been no recent avalanches reported on this layer, however it may be possible to trigger it from shallow, rocky terrain.

Terrain and Travel

  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Avoid freshly wind loaded terrain features.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.