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Avalanche Forecast

Archived

Dec 7th, 2020–Dec 8th, 2020

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

Regions

South Coast Inland.

Rain and wet flurries, wind, and high freezing levels - expect to find changing conditions as you gain elevation and transition above the rain/snow line.

Confidence

Moderate - Uncertainty is due to rapidly fluctuating freezing levels.

Weather Forecast

MONDAY NIGHT: Rain and wet snow, 5-15 cm / Moderate, gusty southwest ridgetop wind / alpine low temperature -1 / Freezing level 2000 m

TUESDAY: Wet flurries and showers, trace to 5 cm / Moderate, gusty southwest ridgetop wind / alpine high temperature +1 / Freezing level dropping to 1500 m

WEDNESDAY: Isolated flurries, trace to 10 cm / Light southwest ridgetop wind / alpine high temperature -3 / Freezing level 1000 m

THURSDAY: Mostly cloudy / Light southwest ridgetop wind / alpine high temperature -4 / 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

Rain and warm temperatures produced moist snow to 1800 m. Above the rain/snow line, Wind is impacting 5-10 cm new snow accumulated by Monday afternoon.

Prior to the storm, a melt-freeze crust covered most surfaces. A variety of wind affected surfaces covered more northerly, alpine terrain. Large surface hoar growth was observed around treeline, but this may have been destroyed by this wet and warm storm.  

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. We have a lot of uncertainty on the reactivity of this layer - we're keeping it on our radar because we don't have enough information. Recent snowpack tests in the Cayoosh zone found this layer present and down 60 cm, and unreactive to snowpack tests. 
  • In the south of the region, treeline snowpack depth sits around 120-190 cm. 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 fresh storm slabs building throughout the day.
  • 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

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.