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Avalanche Forecast

Archived

Dec 4th, 2022–Dec 5th, 2022

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.
Below Treeline
Natural avalanches unlikely.

Regions

Purcells, Dogtooth, East Purcell.

Diligently watch for changing conditions throughout the day. Increasing winds may form fresh, reactive wind slabs in the alpine and treeline.

Small avalanches have the potential to trigger deeper weak layers. Take a cautious approach to risk management and assess conditions as you travel.

Confidence

Moderate

Avalanche Summary

On Saturday, a small (size 1) skier triggered persistent slab avalanche occurred on a northwest aspect at treeline. A larger (size 2) natural slab avalanche was also observed from a distance on an east-facing alpine slope.

Last week, a small (size 1) natural persistent slab avalanche was observed at treeline on a steep, south-facing road bank. It failed on the sugary, faceted layer 25 cm deep.

We have very few eyes out there. If you do get out please consider reporting in the MIN.

Snowpack Summary

Increasing westerly winds may form fresh winds in the alpine and treeline throughout the day. The upper snowpack has been redistributed by variable winds in the past week. In exposed terrain, slopes may have been scoured back significantly. In sheltered areas, 20-60 cm overlies a generally weak, sugary, facetted lower snowpack. A buried layer of surface hoar sits 25-60 cm deep and remains a layer of concern.

The overall height of snow is highly variable throughout the region with around 40-150 cm in the alpine.

Weather Summary

Sunday night

Increasing cloud cover, trace new snow possible in the early morning. Westerly winds strengthening to 25-40 km/h at ridgetop. Treeline temperatures drop to ~ -20 C.

Monday

A mix of sun and cloud, light snowfall possible with trace accumulation. Northwest winds 10-20 km/h at ridgetop. Treeline temperatures reach a high of -13 C.

Tuesday

Cloudy with snowfall, up to 5 cm of accumulation expected. Northwest winds 10-40 km/h at ridgetop. Treeline temperatures reach a high of -15 C.

Wednesday

A mix of sun and cloud, light snowfall possible with trace accumulation. Westerly winds 5-25 km/h at ridgetop. Treeline temperatures reach a high of -10 C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Early season avalanches at any elevation have the potential to be particularly dangerous due to obstacles that are exposed or just below the surface.

Problems

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.

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.