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Avalanche Forecast

Archived

Dec 5th, 2020–Dec 6th, 2020

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

Regions

North Columbia.

Last day of high pressure before the taps turn back on. 

If you're getting sendy, check your line for rogue pockets of wind slab. Getting knocked off your feet can be serious in extreme terrain.

Confidence

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

Weather Forecast

Saturday night: Clear, light to moderate southwest wind, temperature inversion breaking down, freezing level valley bottom.

Sunday: Cloud increasing in the afternoon, light to moderate southwest wind, freezing level 800-1200 m.

Monday: 10-20 cm new snow, moderate southwest wind, freezing level 1100 m.

Tuesday: 20-30 cm new snow, light southwest wind, freezing level 1300 m.

Avalanche Summary

Loose snow avalanches up to size 1.5 were reported on steep solar aspects during the warmup on Wednesday and Saturday.

Our eyes and ears in the mountains are limited this winter due to fewer professional observations. If you go out in the mountains, please share your observations on the Mountain Information Network (MIN). Photos are especially helpful! Thank you so much for all the great MINs submitted so far!

Snowpack Summary

A melt-freeze crust exists on steep solar aspects at treeline and above. On shadier aspects, alpine surfaces are predominantly wind affected, with soft snow still to be found at lower elevations. Widespread growth of large surface hoar crystals and surface faceting have been reported. These types of crystals (crust, hoar, facets) that develop on the surface as it sits exposed during prolonged periods of high pressure like this often become a problem once buried by the next snowfall.

The lower snowpack is characterized by a couple of crusts, the most notable of which is sitting near the base of the snowpack, likely surrounded by a weak layer of sugary facets. It is most likely to be reactive to human triggers on south facing slopes and in shallow, rocky areas in the alpine.

Terrain and Travel

  • When a thick, melt-freeze surface crust is present, avalanche activity is unlikely.
  • Be alert to conditions that change with aspect and elevation.
  • Small avalanches can have serious consequences in extreme terrain. Carefully evaluate your line for wind slab hazard before you commit to it.

Problems

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.