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Avalanche Forecast

Archived

Feb 1st, 2023–Feb 2nd, 2023

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

Regions

Purcells, Dogtooth, East Purcell, West Purcell.

Continue to exercise patience with this snowpack and avoid aggressive terrain choices.

Confidence

Moderate

Avalanche Summary

Small wind slabs continue to be triggered both naturally and with explosive control work, most of these occurrences were in the western part of our region.

Over the weekend a very large natural size 4 deep persistent slab avalanche was reported. This avalanche started as a wind slab in steep rocky terrain and stepped down to the ground.

Snowpack Summary

Wind slabs up to 20 cm in depth can be found on a variety of surfaces including previously wind-affected snow, a small layer of surface hoar, and a sun crust.

Our mid-pack has two layers that remain of concern. The first is down 20 to 40 cm and is a layer of surface hoar from early January. The second, is a layer of surface hoar, facets, and crust down 40 to 60 cm.

A layer from late November is down 70 to 130 cm and is part of a generally weak faceted snowpack. Snowpack depths range between 80 and 180 cm at treeline and are shallowest in the eastern part of our region.

Weather Summary

Wednesday Night

Partly cloudy, flurries 2 to 3 cm of new snow, winds 15 to 20 km/h westerly, treeline temperatures of -8 °C.

Thursday

Mostly clear skies, trace accumulations in the morning, 15 to 20 km/h southwest winds. Treeline temperatures -4 °C.

Friday

Increasing clouds, 2 to 5 cm of new snow starting later in the day, 10 to 20 km/h southwest winds, treeline temperatures -5 °C.

Saturday

Mostly cloudy, 2 to 5 cm new snow, 15 to 20 km/h southwest winds, treeline temperatures -2 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
  • Uncertainty is best managed through conservative terrain choices at this time.
  • Approach lee and cross-loaded slopes with caution.

Problems

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.

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.