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Avalanche Forecast

Archived

Feb 4th, 2023–Feb 5th, 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.

Continue choosing low consequence terrain to play in. A complex, and generally weak snowpack is forcing us to find fun on mellow slopes.

Confidence

Moderate

Avalanche Summary

On Thursday, west of Invermere, a large (size 2.5), naturally triggered Deep Persistent Slab avalanche was reported. It was in the alpine, and it's suspected that it was triggered by a combination of windloading, and morning sun warming the slope.

A few large (size 2) persistent slab avalanches were triggered by explosives over the past few days, releasing about 40 cm deep in alpine terrain.

The possibility remains of triggering facets near the base of the snowpack, particularly on shallow, rocky slopes.

Snowpack Summary

Wind slabs of approximately 20 cm thick may linger on a variety of surfaces including previously wind-affected snow, a small layer of surface hoar, and a melt-freeze crust on sun-exposed slopes.

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

A layer from late November is found 70 to 130 cm deep and is part of a generally weak, faceted snowpack.

Snowpack depths range between 80 and 180 cm at treeline, with the shallowest depths found on the eastern edge of the region.

Weather Summary

Saturday Night

Partly cloudy. No new snow expected. Light southwest ridgetop wind. Treeline temperature around -5 °C.

Sunday

Partly cloudy. No new snow expected. Light southwest ridgetop wind, possibility of strong west at very high elevations. Treeline temperature around -3 °C.

Monday

Mostly cloudy. Possible trace of snow expected. Variable moderate ridgetop winds around the region. Possibility of strong west wind at very high elevations. Treeline temperature around -5 °C.

Tuesday

Partly cloudy. Possible trace of snow expected. Moderate southwest ridgetop wind trending to strong at higher elevations. Treeline temperature around -3 °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.
  • Surface hoar distribution is highly variable. Avoid generalizing your observations.
  • Approach lee and cross-loaded slopes with caution.
  • Uncertainty is best managed through conservative terrain choices at this time.

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.