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Avalanche Forecast

Archived

Dec 18th, 2022–Dec 19th, 2022

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

Regions

Purcells, Dogtooth, East Purcell.

Although avalanche activity has tapered off, buried weak layers are still reactive to rider triggering.

Cold temperatures and shorter days should play a role in your trip plan.

Confidence

Moderate

Avalanche Summary

Avalanche control continues to trigger the mid-November weak layer, producing up to size 2 avalanches. Natural and rider-triggered activity on this layer has died down over the past week but in the neighboring central Columbia region, where it is buried deeper, this layer continues to produce rider-triggered avalanches up to size 2.5. Cold temperatures and little snowfall are not likely going to help heal this layer.

Snowpack Summary

Up to 15 cm overlies variable surfaces ranging from hard old wind slabs in exposed features at upper elevations to soft, unconsolidated facets in sheltered areas.

A concerning weak layer composed of surface hoar, facets, and/or a crust that formed in mid-November is now buried 40 to 80 cm deep. Avalanche activity on this layer has tapered off but it is likely still possible to trigger this layer in isolated terrain features at treeline.

Alpine snowpack distribution is variable, with depths ranging from 70 to 140 cm.

Weather Summary

Sunday Night

Cloudy, up to 2 accumulation, 10 to 15 km/h northeast wind, temperature -25 C at 1500 m.

Monday

A mix of sun and cloud, trace accumulation, 10 km/h northeast winds, temperature -25 C at 1500 m.

Tuesday

Sunny with cloudy periods, no accumulation, 15 km/h southeast wind, temperature -20 C at 1500 m.

Wednesday

Mostly sunny, no accumulation, 10 km/h northwest winds, alpine temperature of -25 to - 30 C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Avoid open slopes and convex rolls at and below treeline where weak layers may be preserved.
  • Keep in mind that human triggering potential persists as natural avalanching tapers off.
  • Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.

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.