Avalanche Forecast

Archived

Jan 5th, 2024–Jan 6th, 2024

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

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

Esplanade, Dogtooth.

Uncertainty about buried weak layers warrants conservative terrain choices.

Confidence

Moderate

Avalanche Summary

Explosive control work over the past week has been consistently triggering large avalanches on buried weak layers with the most recent occurrence on Thursday in the Esplanade.

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

Snowpack Summary

New snow continues to gradually accumulate 5-20 cm 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 in the Dogtooth and 60 to 90 cm deep in the Esplanade ranges. It is a concern at elevations (generally above 2000 m) where it is not bridged by a hard crust.
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

Friday night

Cloudy with 5-10 cm of new snow, southwest alpine wind 30 km/h, treeline temperature -10°C.

Saturday

Mostly cloudy with a few centimeters of new snow, southwest alpine wind 15 km/h, treeline temperature -7°C.

Sunday

Up to 5 cm of new snow overnight then clearing to a mix of sun and cloud, southwest alpine wind 10 km/h, treeline temperature -8 °C.

Monday

A mix of sun and cloud, southwest alpine wind 20 km/h, treeline temperature -9 °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

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

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.

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.