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Avalanche Forecast

Archived

Dec 6th, 2020–Dec 7th, 2020

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

Regions

Sea To Sky.

A wet and warm storm will drop upwards of 25-50 cm through Monday. Along with strong, gusty winds and spiking freezing levels, expect rapid storm slab development and avalanche hazard increasing to HIGH near the end of the day.

Confidence

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

Weather Forecast

SUNDAY NIGHT: Flurries and snow, 5-10 cm by morning / Moderate, increasing to strong, south-southwest ridgetop wind / alpine low temperature -3 / Freezing level 1400 m

MONDAY: Snow, 20-50 cm / Strong, south-southwest ridgetop wind / alpine high temperature +1 / Freezing level rising to 2100 m

TUESDAY: Snow and flurries, 10-30 cm / Moderate, gusty southwest ridgetop wind / alpine high temperature -2 / Freezing level 2100 m and dropping

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

Avalanche Summary

Outside of a few small loose-wet avalanches from steep terrain, there have been no avalanche observations since last Wednesday (Nov 2) when natural widespread wet loose avalanche cycle up to size 3 was triggered by warming.

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. The snowpack depth varies with elevation. Below treeline 30 to 70 cm, 80 to 100 cm near treeline, and over 150 cm may be found in the alpine.

The mid to lower snowpack contains a series of crusts, the most notable of which is also the deepest, sitting just above the ground at elevations above 1500 m. This crust may have a thin overlying layer of weak faceted grains and/or surface hoar crystals, especially in sheltered areas around treeline. The incoming storm may provide insight on if these layers will be a concern going forward. 

Terrain and Travel

  • Storm slab size and sensitivity to triggering will likely increase through the day.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
  • 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.