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Avalanche Forecast

Archived

Dec 16th, 2020–Dec 17th, 2020

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

Cariboos.

New snow on a buried weak layer will become increasingly reactive to human triggers, especially where impacted by wind.

Confidence

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

WEDNESDAY NIGHT - Mainly cloudy with isolated flurries, up to 10 cm / southwest wind, 20-50 km/h / alpine high temperature near -7 

THURSDAY - Mainly cloudy with flurries, 5 cm / southwest wind, 25-45 km/h / alpine high temperature near -8 

FRIDAY - Mainly cloudy with flurries, 5-15 cm / southwest wind, 45-65 km/h / alpine high temperature near -5

SATURDAY - Mainly cloudy with flurries, 10-20 cm / southwest wind, 45-70 km/h / alpine high temperature near 0

Avalanche Summary

New snow and moderate to strong southwest winds have likely formed slabs that will probably be reactive to human triggers, especially in wind loaded areas, and in places that have seen more than 20 cm of new snow accumlate.

Several large natural avalanches were reported last Friday at Chappel Creek (see this MIN report). These avalanches occurred on south aspects at treeline elevations. Based on the depth of these avalanches, they likely failed on recently buried surface hoar and/or sun crust layers. 

Snowpack Summary

About 10-30 cm of new snow has accumlated around the Cariboos, with a few exceptions receiving up to 40 cm (mostly around Blue River). This low density snow has buried a layer of surface hoar in many areas. Expect to find more reactive slabs as new snow accumlates and gains cohesion.

A weak layer that was buried about a week ago is now down 30-60 cm. In many areas the weak layer exists as a crust, and in some areas, it has been found as surface hoar. There is uncertainty as to how well the new snow may be bonding to this layer.

Near the base of the snowpack is a crust that was buried in early November. This crust likely has weak facets associated with it. There have been no recent avalanches reported on this layer, though it may be possible to trigger 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.
  • Investigate the bond of the recent snow before committing to your line.

Problems

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.