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Avalanche Forecast

Archived

Jan 18th, 2022–Jan 19th, 2022

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

Regions

Lizard-Flathead.

Riding conditions are improving with new fresh snow, but be mindful of the deep persistent slab problem. Use caution on shallow snowpack areas and thin to thick steep rocky zones. 

Confidence

High - Confidence is due to a stable weather pattern with little change expected.

Weather Forecast

TUESDAY: Cloudy periods, light variable wind, treeline high around -10 C, freezing level returning to valley bottom.

WEDNESDAY: Sunny with cloudy periods, light southwest wind, treeline high around -12 C, freezing level returning to valley bottom.

THURSDAY: Snow up to 5 cm, moderate-strong southwest wind, treeline high around -5 C, freezing level rising to 1000 m.

FRIDAY: A mix of sun and cloud; light variable wind, treeline high around -5 C, freezing level rising to 1000 m.

Avalanche Summary

A wind slab avalanche was released naturally on steep north-facing wind-loaded alpine terrain on Tuesday on Lizard Peak.

A near-miss happened this weekend on Tombstone mountain when a rider triggered a large persistent slab and got completely buried. Luckily, the airbag helped keep the victim's head above the snow. This evidence suggests the deep persistent slab problem is still a concern in the region.

Snowpack Summary

Fresh dry snow (5-10 cm) is present at upper elevation, covering older wind-affected / crusty surfaces. Around 2000 m and below, a crust is now capping the dense 15 cm of snow which has settled significantly with the past mild temperatures. The crust varies from thin/breakable to thick/supportive, according to the aspects and elevation. Under it, the snowpack consists of a variety of old surfaces, including soft snow in sheltered areas and wind slabs in exposed and open areas.

The most notable layer of concern in the snowpack is a crust that was formed in early December and is now down 100-270 cm. This layer appeared to have "waken up" in response to warm temperatures and solar radiation on Thursday Jan 13, when at least three very large avalanches were reported on this layer. This layer has created a low likelihood, high consequence scenario which is best managed through conservative terrain choices and disciplined backcountry travel techniques.

Terrain and Travel

  • Investigate the bond of the recent snow
  • Recent new snow may be hiding windslabs that were easily visible before the snow fell.
  • Be aware of the potential for large avalanches due to the presence of a deep persistent slab.
  • Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.

Problems

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.