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Avalanche Forecast

Archived

Dec 8th, 2021–Dec 9th, 2021

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

Regions

Yukon.

It's a good time to go out, assessing slopes as you travel. If you get into wind affected terrain watch for windslabs, shooting cracks and drumming sounds. Thin snowpack areas are where you're most likely to tickle the basal weakness so don't have snowy slopes above you. 

Confidence

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

A quiet Thursday followed by stormy Friday

WEDNESDAY NIGHT: Light winds and precipitation ending. Temperatures have fallen to -10C and should continue dropping to around -15C overnight.

THURSDAY: Broken cloud cover, daytime high temp around -12 C, light wind generally out of the southwest, no snow expected.South winds expected to crank up Thursday night.

FRIDAY: The day will arrive with a bang: strong to extreme winds and around 10 cm of snow. A bit more during the day. as the storm and wind wind down. High temp around -10 C.

SATURDAY: Broken or overcast sky, light north east wind, a few flurries, and cooling temperatures nudging towards -20's C.

Avalanche Summary

Our AvCan field team reports whumpfs and shooting cracks up to 10 m from thin snowpack areas in the Fraser Chutes today (Wednesday).

Snowpack Summary

A drawing of my mental map of the snowpack is available here.

Terrain and Travel

  • Start with conservative lines and watch for clues of instability.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.

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.

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.