Avalanche Forecast

Archived

Feb 27th, 2024–Feb 28th, 2024

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural and human triggered avalanches likely.

Below Treeline

Natural avalanches possible, human triggered probable.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

Purcells, Dogtooth, East Purcell.

As new snow accumulates avalanche hazards will increase. Continue to give new snow time to settle and stabilize.

Confidence

Moderate

Avalanche Summary

Numerous natural, skier, and explosive-triggered avalanches were reported on Monday throughout the region. All avalanches slid on layers in the upper snowpack, up to 70 cm deep.

Snowpack Summary

As much as 50 cm of recent snowfall has buried various old surfaces, including faceted snow or surface hoar in north-facing terrain and sun crusts on south-facing slopes.

A widespread crust formed in early February is buried roughly 40 to 80 cm. In some areas, weak faceted crystals have formed above or below the crust, creating a problematic layer.

The mid and lower snowpack is largely faceted with depth hoar and a crust found at the bottom of the snowpack in many areas.

Weather Summary

Tuesday Night

Partly cloudy with 0 to 5 cm of snow. 20 to 40 km/h west ridgetop wind. Treeline temperature -16 °C.

Wednesday

Mix of sun and cloud with 5 to 10 cm of snow. 30 to 50 km/h southwest ridgetop wind. Treeline temperature -10 °C. Freezing level 1400 m.

Thursday

Mostly cloudy with 5 to 10 cm of snow. 20 to 40 km/h southwest ridgetop wind. Treeline temperature -4 °C. Freezing level 1600 m.

Friday

Mix of sun and cloud with 0 to 2 cm of snow. 20 to 40 km/h southwest ridgetop wind. Treeline temperature -10 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

Good day to make conservative terrain choices.
Be aware of the potential for large, destructive avalanches due to the presence of deeply buried weak layers.
In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.

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.