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Avalanche Forecast

Archived

Jan 6th, 2024–Jan 7th, 2024

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

Regions

Dogtooth.

Avoid areas where the snowpack is thin and rocky. Weak layers are most triggerable here.

Confidence

Low

Avalanche Summary

Explosive control work over the past week has triggered large avalanches on buried weak layers. This includes reloaded bed surfaces of previous avalanches (where the snowpack becomes more faceted and weaker).

Last weekend, a skier in the Dogtooth Range accidentally triggered a size 2 deep persistent slab on basal facets over a smooth rock slab.

While avalanche activity has decreased these layers remain possible for human triggering with high consequences.

Snowpack Summary

New snow continues to gradually accumulate over old surfaces including crusts, facets and surface hoar. Beneath lies a complex snowpack with several layers of concern.

  • A layer of surface hoar is buried 40 to 70 cm deep. It is a concern at elevations (generally above 2000 m) where it is not bridged by a hard crust above.

  • Weak basal facets characterize the lower snowpack, especially in alpine terrain.

Read this blog post for more details.

Snowpack depths at treeline range from 60 to 130 cm.

Weather Summary

Saturday Night

Mostly cloudy with 5-10 cm of snow. Freezing levels at valley bottom. Light and variable winds.

Sunday

Mostly cloudy with a possible afternoon sun. Northwest winds, 10-20 km/h. Freezing levels at valley bottom. Treeline temperature -8 °C.

Monday

Partly cloudy, westerly winds 20-30 km/h. Freezing levels at valley bottom, treeline temperature -12 °C.

Tuesday

Partly cloudy, southwest winds 20-50 km/h. Freezing levels at valley bottom, treeline temperature -7 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Uncertainty is best managed through conservative terrain choices at this time.
  • Be mindful that deep instabilities are still present and have produced recent large avalanches.
  • Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
  • Closely monitor how the new snow is bonding to the old surface.

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.

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.