Avalanche Forecast

Issued: Dec 19th, 2020 4:00PM

The alpine rating is high, the treeline rating is high, and the below treeline rating is considerable. Known problems include Storm Slabs and Persistent Slabs.

Avalanche Canada ghelgeson, Avalanche Canada

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The upper snowpack is a mess and the incoming 15 to 25 cm of new snow is expected to be accompanied by strong wind. A natural avalanche cycle is likely overnight & may persist into Sunday. Travel in avalanche terrain is not recommend Sunday.

Summary

Confidence

Moderate - Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.

Weather Forecast

The storm parade continues for the foreseeable future.

SATURDAY NIGHT: Freezing level around 1000 m, strong southwest wind, 15 to 25 cm of snow expected.

SUNDAY: Overcast, freezing level around 1200 m, strong west/southwest wind, 5 to 10 cm expected through the day.

MONDAY: Overcast, freezing level around 900 m, light south wind with moderate gusts at ridgetop, 20 to 30 cm of snow possible.

TUESDAY: Scattered cloud cover, freezing level near valley bottom, light to moderate northerly wind at ridgetop, no precipitation expected.  

Avalanche Summary

New snow and wind Saturday night into Sunday are expected to initiate a natural avalanche cycle that may persist into Sunday.

On Friday touchy storm slabs to size 2 continued to be reported, check out all of the MIN Reports for the region here. In the Gold Range of the Monashees a size 2.5 natural avalanche stepped down to the early December crust Friday night on a convex south facing feature around 2000 m.

Storm and wind slabs were underfoot/sled on Thursday (MIN report). Explosives triggered avalanches to size 2 along ridgelines and with good connectivity. Skiers reported reactive slabs 20-50 cm deep, most within the storm snow and in one case, steeping down to the early December crust.

A handful of natural avalanches were reported including one notable size 3 avalanche near Monashee Provincial Park - a 30-60 cm deep wind slab that failed on the early December crust, running for 1000 m.

Snowpack Summary

Ongoing flurries and snow has accumulated 30-50 cm fresh snow around the region. This new snow has buried a weak layer of surface hoar in many areas. This new snow combined with southwest winds has formed reactive slabs, especially at higher elevations. 

A weak layer that was buried in early December is now down 30-60 cm. This layer is variable and has been reported to exist as either a crust with facets or surface hoar. In any case, it is a persistent weak layer with a significant load above it now, and it may react easily to human triggers.

This MIN report from Thursday really captures the snowpack well, and documents reactivity both within the storm snow and on the early December crust.

Another crust that was buried in early November can be found near the base of the snowpack. There have been no recent avalanches reported on this layer, however it may be possible to trigger it from shallow, rocky terrain.

Terrain and Travel

  • Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Avoid freshly wind loaded terrain features.
  • Only the most simple non-avalanche terrain free of overhead hazard is appropriate at this time.

Problems

Storm Slabs

An icon showing Storm Slabs

Look for the formation of fresh, sensitive storm slabs as strong southwest wind and 15 to 25 cm of new snow come together Saturday night into Sunday. This snow will add to the 30 to 50 cm that already rests on the surface hoar.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1.5 - 2.5

Persistent Slabs

An icon showing Persistent Slabs

This storm may well push the persistent slab problem over the tipping point resulting in large and surprisingly touchy avalanches. The slab rests on a persistent weak layer which has the capacity to propagate avalanches across terrain features. Wind exposed features are expected to be particularly volatile.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

2 - 3.5

Valid until: Dec 20th, 2020 4:00PM