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Avalanche Forecast

Archived

Jan 30th, 2022–Jan 31st, 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 unlikely, human triggered possible.
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

Purcells.

New wind slabs are expected to be touchy on Monday, especially where they overlie surface hoar or a crust. Loose dry avalanches should be expected on steep slopes.

Confidence

Low - Uncertainty is due to the timing, track, & intensity of the incoming weather system.

Weather Forecast

A storm system brings snowfall to the region Sunday night which may linger through the early part of the day on Monday. Modelled snowfall amounts and timing are highly variable which is creating a lot of uncertainty for conditions on Monday. 

Sunday Night: Snowfall 10-20 cm, moderate SW wind, treeline temperature around -6 C°.

Monday: Snowfall up to 5 cm in the morning, sunny breaks in the afternoon, light to moderate W-NW wind, treeline high around -4 C°.

Tuesday: A mix of sun and cloud, light NW wind, treeline high around -6 C°.

Wednesday: Mainly sunny, light variable wind, treeline high around -10 C°.

Avalanche Summary

On Saturday, a skier triggered a size 1.5 wind slab on an E aspect in the alpine which failed down 5-20 cm. On Friday, explosives triggered a size 1 slab on a north aspect near treeline which failed on a reloaded bed surface of the early December interface. A skier and explosives also triggered a couple wind slabs in very steep terrain and explosives triggered a cornice which scrubbed a gully down to the ground. Some solar triggered loose avalanches were also reported on steep rocky slopes. 

Avalanche activity on the early-December weak layer described in the snowpack summary has been sporadic over the past few weeks. Prior to this most recent drought, we were tending to see reports of avalanches on this layer every few days. Most of the avalanches occurred at elevations around 2000 m. Possible natural triggers include daytime warming, warming from the sun, cornice falls, or smaller avalanches stepping down. Human triggering is most likely in steep, rocky slopes with a shallow or thin-to-thick snowpack.

Snowpack Summary

The new snow is burying a highly variable snow surface which consists of wind affected surfaces in exposed high elevation terrain, a melt freeze crust at lower elevations and on solar aspects extending into the alpine, and/or widespread surface hoar in sheltered areas which is appears to typically be 5-15 mm. 

Some older thin surface hoar layers are 20-40 cm deep, but have not been producing concerning results in recent snowpack tests. 

The most notable layer of concern in the snowpack is a facet/crust layer that formed in early December and ranges in depth between 70 cm along the shallower eastern Purcells and up to 150 cm in the western Purcells. This recent blog post goes into more details on this interface and why it is expected to continue to create problems for the rest of the season. 

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Be aware of the potential for loose avalanches in steep terrain where snow hasn't formed a slab.
  • Conditions may have improved, but be mindful that deep instabilities are still present.

Problems

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.