Avalanche Forecast

Archived

Nov 23rd, 2019–Nov 24th, 2019

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 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

South Columbia.

30+ cm of new snow is expected in the northern parts of the region, which will likely result in two things:

1. A touchy storm slab problem

2. Potentially wake up the persistent slab problem

Choose simple terrain on Sunday as the snowpack adjusts to the load of new snow.

Confidence

No Rating - Uncertainty is due to the complexity of the snowpack’s structure. Uncertainty is due to how the snowpack will react to the forecast weather. Uncertainty is due to the limited number of field observations.

Weather Forecast

Saturday night: Another 10-20 cm of snow above 1400 m with moderate to strong southwest winds.

Sunday: Broken cloud cover, moderate winds shifting to the west/northwest, freezing level around 1000 m and dropping, continued flurries with 5-10 cm of additional accumulation possible

Monday: Clearing skies, freezing level near valley bottom, light northwest winds, no significant precipitation expected.

Tuesday: Clear, calm, cold, dry.

Avalanche Summary

Very little avalanche activity has been reported over the last week, but anticipate another avalanche cycle this weekend. As storm snow accumulates, human-triggered avalanche activity is likely.

If you see anything while out in the field, please consider sharing that information with us and the backcountry community via the Mountain Information Network (MIN).

Snowpack Summary

Winter ramps up this weekend as the latest storm brings fresh snow, heightened avalanche hazard, and a good test for our snowpack.

Snow totals of around 30 cm should accumulate by Sunday morning, with winds primed for snow transport. The northern parts of the region should see the highest snowfall amounts. The new snow is unlikely to bond well with the previously wind-affected surfaces in the alpine and with the crust and surface hoar that developed near and below tree line. This rapid load may also trigger deeper weak layers formed in mid-November and late October that are now down 40-80 cm.

This storm brings winter lower into the valleys, as snowline could drop to 1000 m. Current total snowpack depths range from about 60 cm below treeline to as high as 170 cm in the alpine.

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.