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Avalanche Forecast

Archived

Feb 8th, 2022–Feb 9th, 2022

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

Regions

Purcells.

Keep an eye on the snow surface, as it gets moist the likelihood of triggering avalanches will increase. Avoid overhead hazards.

Confidence

Moderate -

Weather Forecast

Tuesday night: low of -4 at 1700m. A possibility of light flurries bringing trace amounts of snow. Moderate west winds.

Wednesday: A mix of sun and cloud with moderate to strong northwest winds. Freezing levels rising to 2200m.

Thursday: Mainly sunny with light to moderate W wind. Freezing levels reaching over 2500 m with an inversion.

Friday: Freezing levels around 1600m with no new snow expected. Light northwest winds.

Avalanche Summary

On Sunday, several natural wind slabs and loose avalanches were reported. A skier remotely triggered a size 1.5 wind slab from 3 m away on an east aspect at 2500 m. Explosives triggered a number of slab avalanches size 1.5-2.5 in the deeper west part of the region where the slab thickness was typically 30-50 cm and up to 120 cm in wind loaded terrain. 

This MIN post from the Dogtooth shows the type of open slopes where the buried surface hoar may be reactive at lower elevations. 

On Saturday, several natural wind slabs up to size 1.5 were reported throughout the region. Ski cuts triggered a couple small slabs and some small loose avalanches in steep terrain. A skier remotely triggered a size 1.5 slab from 5 m away on a west aspect at 1900 m which failed on the late-January surface hoar down 55 cm in the deeper western part of the region. Explosives triggered a size 2 cornice which released a slab on the slope below. 

Snowpack Summary

As the freezing levels rise moist snow may be observed on all aspects at and below treeline as well as south facing slopes in the alpine.

A new sun crust is being reported on solar aspects into the alpine and a temperature crust on all aspects at lower elevations. Ongoing periods of strong wind from the southwest through northwest have formed reactive wind slabs in exposed terrain at higher elevations. 

The January 30 interface is now typically down 20-40 cm and consists of a melt-freeze crust at lower elevations and on solar aspects extending into the alpine, surface hoar in sheltered areas at and below treeline, and small facets in some areas.

Several old surface hoar layers are now buried in the upper snowpack 40-70 cm deep. While these old layers appear to have gone dormant, there is still an isolated chance of avalanches stepping down to a deeper layer. 

The early December crust/facet layer of concern sits around 80 cm deep in the eastern Purcells and shallow terrain, and up to 150 cm in the west. This layer produced numerous large avalanches in January but is now considered dormant. See this forecaster blog on how to manage this layer as it may come into play again later this season. 

Terrain and Travel

  • Be aware of the potential for large avalanches due to the presence of buried weak layers.
  • Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent avalanches.
  • Back off slopes as the surface becomes moist or wet with rising temperatures.
  • Avoid exposure to slopes that have cornices overhead.
  • Be careful as you transition into wind affected terrain.

Problems

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.