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Avalanche Forecast

Archived

Jan 19th, 2022–Jan 20th, 2022

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

Regions

Lizard-Flathead.

Reactive wind slabs may build on Thursday with new snow, strong wind and warmer temperatures.

Be mindful of the lingering deep persistent slab problem. Caution on shallow snowpack areas and thin to thick steep rocky zones.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Thursday Night: Increasing cloud cover later in the evening with some new snow forecast up to 5 cm. Ridgetop wind light from the southwest and alpine temperatures near -10. 

Thursday: Snow 5-10 cm accompanied by moderate ridgetop wind from the southwest. Alpine temperatures warming to near -5 and freezing levels 1200 m.

  

Friday: Mostly cloudy with ridgetop winds moderate from the West. Alpine temperatures near -5 and freezing levels valley bottom.

Saturday: Potential for inversion with valley cloud and cooler temperatures down low and sunshine in the alpine. Alpine temperatures near -3 and below freezing in the valleys.

Avalanche Summary

On Wednesday, no new avalanches were reported in the region.

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

5 cm of new snow fell overnight with an additional 10 cm in the forecast. This sits above older wind-affected and crusty surfaces. Around 2000 m and below, a crust is now capping the dense 15 to 30 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. The midpack is well consolidated. 

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 was last reactive on Thursday, Jan 13 with warming and solar radiation. 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

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Watch your sluff: it may run faster and further than you expect.
  • In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.
  • Be aware of the potential for large avalanches due to the presence of a deep persistent slab.

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.