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Avalanche Forecast

Archived

Dec 6th, 2020–Dec 7th, 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, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.

Regions

South Coast Inland.

With new flurries and wind, keep a look out for wind slabs building through the day.

Confidence

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

Weather Forecast

SUNDAY NIGHT: Cloudy and flurries, up to 5 cm / Moderate to strong, southwest ridgetop wind / alpine low temperature -4 / Freezing level 1200 m

MONDAY: Flurries and wet snow, 5-15 cm / Strong, southwest ridgetop wind / alpine high temperature +1 / Freezing level rising to 2000 m

TUESDAY: Flurries, 5-15 cm / Moderate, gusty southwest ridgetop wind / alpine high temperature +1 / Freezing level dropping to 1500 m

WEDNESDAY: Isolated flurries / Light southwest ridgetop wind / alpine high temperature -3 / Freezing level 1000 m

Avalanche Summary

On Saturday, a few wet loose avalanches to size 2 were observed from steep rocky features in the sun. Outside of a few other small wet loose avalanches from steep terrain, there have been no avalanche observations since last Wednesday (Nov 2) when a widespread wet loose avalanche cycle up to size 2 was triggered by warming.

Of note to consider in the Duffy area: A notable avalanche occurred last Tuesday (Nov 1) when 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

A melt-freeze crust covers most slopes resulting from recent sun and warm temperatures. Where cold, dry snow prevailed (upper elevations on more shaded and polar slopes), winds continue to press slabs into lee features. Large surface hoar growth has been observed in treeline areas sheltered from the warm temperatures, sunshine and wind.  

The lower snowpack is characterized by a few crusts that formed during warm periods in November. 

  • In the north, treeline snowpack depth sits around 80 to 150 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, treeline snowpack depth sits around 120-190 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

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Be alert to conditions that change with elevation and wind exposure.
  • Back off slopes as the surface becomes moist or wet with rising temperatures.
  • When a thick, melt-freeze surface crust is present, avalanche activity is unlikely.

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.

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.