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Avalanche Forecast

Archived

Dec 5th, 2020–Dec 6th, 2020

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

Regions

South Coast Inland.

As you transition from melt-freeze conditions to dry snow, be on the lookout for wind-loaded pockets in lee features. And the possibility of wet loose avalanches will persist where snow is moist or wet.

Confidence

Low - Uncertainty is due to the timing, track, & intensity of the incoming weather system. Uncertainty is due to the limited number of field observations.

Weather Forecast

SATURDAY NIGHT: Increasing clouds / Moderate, southwest ridgetop wind / alpine low temperature -8 / Freezing level dropping gradually to 1000 m.

SUNDAY: Cloudy and wet flurries, up to 5 cm / Moderate to strong, southwest ridgetop wind / alpine high temperature +1 / Freezing level 1500 m.

MONDAY: Wet snow, 10-20 cm. / Strong, southwest ridgetop wind / alpine high temperature 0 / Freezing level rising to 2000 m.

TUESDAY: Snow and rain, 10-20 cm. / Moderate, gusty southwest ridgetop wind / alpine high temperature +1 / Freezing level 2000 m.

Avalanche Summary

No new avalanche observations submitted on Thursday or Friday.

On Wednesday, the northern part of the region, several natural avalanches were reported up to size 2 with some older ones from the previous storm up to size 2.5. A couple of isolated natural glide crack avalanches up to size 1.5 were also reported. In the southern half, numerous natural wet loose avalanches occurred up to size 2 mostly from southerly aspects.

Last Tuesday, a large size 3 natural avalanche was observed on a NE aspect at 2400 m. It was reported as a cornice failure triggering the slope below and appeared to have slid on the early November crust near the base of the snowpack.

Have you been out and about in the mountains? If so please submit to the Mountain Information Network (MIN). It doesn't have to be technical it can be as simple as a photo. Photos are especially helpful! Sending out a big thank you to the already submitted MIN's this season. Thanks everyone!

Snowpack Summary

Recent sun and warm air well into the alpine had the greatest impact on the upper snowpack, melt freeze conditions exist on most aspects and elevations. Where dry snow prevails, such as shaded alpine and upper treeline slopes, wind slabs have developed on leeward terrain.

Large surface hoar growth has been reported slopes sheltered from the warm temperatures, sunshine and wind.  

The lower snowpack is characterized by a few crusts that formed during warm periods over the last month. 

  • In the north, treeline snowpack depth sits around 80 to 120 cm. The crust of note here is sitting near the base of the snowpack, likely surrounded by a weak layer of sugary facets. Snowpack tests and recent avalanche activity suggest that this layer could be triggered by humans and produce large avalanches.
  • In the south of the region, the snow line has been reported around 700 m near Hope, and treeline snowpack depth sits around 80-150 cm. Melt-freeze snow surfaces exist after the recent warming. The deeper crusts in this area are generally down around 60-80 cm in the alpine and well bonded to surrounding snow.

Terrain and Travel

  • Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
  • Be alert to conditions that change with elevation and wind exposure.
  • Back off slopes as the surface becomes moist or wet with rising temperatures.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.

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.