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Avalanche Forecast

Archived

Dec 3rd, 2020–Dec 4th, 2020

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

Regions

South Columbia.

Alpine temperatures dip back down to a more seasonal sub-zero in a brief cooling trend Friday. The sun will be shining so still keep an eye on those steep south-to-west slopes in the afternoon, as solar triggered loose snow avalanches are still possible.

Confidence

Moderate - Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack.

Weather Forecast

Thursday night: Clear, light northwest wind, temperature inversion dissipating, freezing level valley bottom.

Friday: Sunny, light northwest wind, disagreement between models has freezing levels somewhere between valley bottom and 1500 m for most of the day. The strong temperature inversion re-establishes in the afternoon with above freezing air 2000-3000 m.

Saturday: Sunny, light southeast wind, strong temperature inversion returns with above freezing air 2000-3500 m.

Sunday: Sunny, light southeast wind, strong temperature inversion with above freezing air 2000-3500 m starting to break down.

Avalanche Summary

Loose wet avalanches up to size 2 were reported on steep solar aspects during the warmup on Wednesday. A size 1 skier controlled wind slab avalanche was also reported on a northeast aspect.

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

Solar radiation coupled with a strong temperature inversion has formed a melt-freeze crust on solar aspects at treeline and above. Alpine surfaces are predominantly wind affected, with soft snow still to be found in shady, protected areas at lower elevations.

A couple of layers of feathery surface hoar crystals exist in the upper snowpack. Just 10 cm below the surface, the first of these layers has likely broken down in areas where the surface warmed up on Wednesday. Another patchier layer of smaller crystals may sit beneath 20-40 cm of old wind slab.

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

  • Minimize exposure to sun-exposed slopes when the solar radiation is strong.
  • Be alert to conditions that change with aspect and elevation.
  • Conditions may have improved, but be mindful that deep instabilities are still present.

Problems

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

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.