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Avalanche Forecast

Archived

Dec 29th, 2024–Dec 30th, 2024

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

Purcells, Crawford, Dogtooth, East Purcell, Moyie, St. Mary, West Purcell.

Persistent slabs are the main concern.

Riders may be able to trigger large slab avalanches from rocky, wind-affected areas.

Confidence

Moderate

Avalanche Summary

On Saturday, explosive control produced wind slab avalanches (size 1.5) in lee alpine terrain near Golden.

On Friday, numerous natural slabs (up to size 2) and loose dry avalanches were reported throughout the region from steep alpine and treeline terrain.

If you head out in the backcountry, let us know what you are seeing by submitting a MIN report!

Snowpack Summary

15 to 30 cm of recent snow exists in sheltered areas. Southwest wind has redistributed this new snow, forming deeper deposits on leeward slopes at higher elevations.

A weak layer buried in early December is now about 40 to 90 cm below the surface. This layer varies, of weak surface hoar or facetted crystals on shaded slopes and a sun crust with facets on south-facing slopes. Professionals are still concerned about the potential instability of this layer.

The base of the snowpack is made up of a thick crust and facets in many areas.

Weather Summary

Sunday Night

Mostly cloudy with up to 5 cm of new snow. 10 to 20 km/h northeast ridgetop wind. Treeline temperature -8 °C.

Monday

A mix of sun and cloud, with isolated flurries. 10 to 20 km/h west ridgetop wind. Treeline temperature -10 °C.

Tuesday

A mix of sun and cloud, with isolated flurries. 10 to 20 km/h southwest ridgetop wind. Treeline temperature -12 °C.

Wednesday

A mix of sun and cloud, with isolated flurries. 20 to 30 km/h southwest ridgetop wind. Treeline temperature -14 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Avoid shallow snowpack areas, rocky outcrops, and steep terrain where triggering is most likely.
  • Be especially cautious as you transition into wind-affected terrain.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

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.