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Avalanche Forecast

Archived

Dec 14th, 2021–Dec 15th, 2021

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 unlikely, human triggered possible.
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

Lizard-Flathead.

The best riding and the lowest avalanche danger can be found in sheltered terrain at treeline and below. The calmer weather should give the snowpack some time to gain strength, but we are still monitoring some lingering avalanche problems.

Confidence

Moderate - We are confident about the possible sizes of avalanches, should one release; what is less certain is the likelihood of triggering.

Weather Forecast

Cloud and light snowfall persist for most of the forecast period, with a possible shot of sun near the end of the week.

TUESDAY NIGHT: Mostly cloudy. 0-5 cm of snow expected. Moderate southwest wind, trending to strong in the alpine. Freezing level dropping to valley bottom.

WEDNESDAY: Mostly cloudy with possible clear periods. Possible trace of snow. Light southwest wind trending to moderate westerly at higher elevations. Warming through the day, alpine temps around -9 C.

THURSDAY: Mostly cloudy. 1-5 cm of snow expected. Moderate southwest winds, with strong westerlies in the alpine. Alpine high around -8.

FRIDAY: Clear morning, scattered cloud in the afternoon. No new snow expected. Alpine high around -8.

Avalanche Summary

On Tuesday, avalanche control with explosives produced numerous size 1-1.5 avalanches in the recent storm snow.

This MIN report has details of a natural size 2.5 avalanche in an East facing treeline feature.

Snowpack Summary

The snowpack varies greatly across the region.

 This post from the Mountain Information Network (MIN), paints a clear picture of the conditions at McLatchie Ridge.

This MIN post from our South Rockies field team, who headed to the Corbin area, has some great conditions and snowpack info.  

The top 20-30 cm of the snowpack is likely, low density, unconsolidated snow. 

This overlies denser snow from the previous storm that fell with more wind. This denser, slabby snow was quite reactive earlier this week, but it does seem to be gaining strength and starting to bond to the early December crust that is now 60-100 cm below the surface. This crust is likely 20 cm thick (or more), and can be found on all aspects below 2400m.

This thick crust is likely to encourage facet formation above and below itself, so it will remain a layer to watch. 

The lower snowpack consists of various early season crusts, and could still be moist from early season rain events.

Snowpack depths range from 55-170 cm at treeline elevations. The snowpack tapers quickly below 1800m.

Terrain and Travel

  • Don't be too cavalier with decision making, storm slabs may remain sensitive to human triggering.
  • Use conservative route selection and resist venturing out into complex terrain.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • Make observations and assess conditions continually as you travel.

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.