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Avalanche Forecast

Archived

Dec 30th, 2020–Dec 31st, 2020

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

Regions

South Columbia.

  

Recently formed storm slabs will be most reactive in wind affected areas at treeline and above. Be especially cautious as you transition into wind affected terrain.

Confidence

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

Weather Forecast

  

WEDNESDAY NIGHT: Cloudy with isolated flurries; 0-3 cm. / Light, southwest ridgetop wind / alpine low temperature -12 / Freezing level valley bottom.

THURSDAY: Cloudy. / Light, northwest ridgetop wind / alpine high temperature -6 / Freezing level valley bottom.

FRIDAY: Cloudy with flurries; 3-5 cm. / Strong, southwest ridgetop wind / alpine high temperature -5 / Freezing level rising to 900 m.

SATURDAY: Snow; 10-15 cm. / Strong, southwest ridgetop wind / alpine high temperature -4 / Freezing level 1300 m.

Avalanche Summary

On Monday, a couple skier triggered storm slab avalanches up to size 1.5 were reported on north and south aspects at treeline in the Monashees south of Revelstoke.

There have been numerous recent reports of dry loose avalanches(sluffs) running surprisingly fast and far below treeline.

Snowpack Summary

  

30-50 cm. of new snow since Christmas day fell on a mixture of faceted old snow and small surface hoar. The recent snow has been slow to settle into a slab and made for some great riding in many areas. This recent snow is most likely to be reactive in wind affected areas where the snow has been stiffened into a slab.

 Two persistent weak layers buried in early/mid Dec. are now 80 to 150 cm below the surface. The form and distribution of these layers are HIGHLY VARIABLE and have created conditions that can vary significantly from one valley to the next. The first layer down around a metre has been primarily reported as small surface hoar. The next layer has been reported as a thin freezing rain crust, surface hoar, or thick rain crust depending on elevation and location. As a result, diligent investigation of the snowpack is required to get a handle on localized conditions.

Terrain and Travel

  • Uncertainty is best managed through conservative terrain choices at this time.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Be especially cautious as you transition into wind affected terrain.
  • Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.