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Avalanche Forecast

Archived

Feb 6th, 2023–Feb 7th, 2023

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, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
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 Sunday, across the region, several small (size 1-1.5) windslab avalanches were reported on various aspects in the alpine and at treeline. They were either triggered naturally, or by the weight of a rider on the slope.

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.

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

Snowpack Summary

20-50 cm of snow since late January is settling, or has been redistributed by moderate southwest wind. This overlies another layer of windslab, or surface hoar sitting on facets or a thin sun crust.

50-70 cm below the surface, the mid-pack contains a layer buried in early to mid January that remains a concern. It mostly exists as surface hoar, but facets or a crust may also be present.

A layer from late November is found 75 to 150 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

Monday Night

Partly cloudy. Possible trace of snow expected. Light to moderate southwest ridgetop wind, possibility of strong west at very high elevations. Treeline temperature around -5 °C.

Tuesday

Partly cloudy. 0-3 cm of snow expected. Light to moderate southwest ridgetop wind trending to strong at higher elevations. Treeline temperature around -3 °C.

Wednesday

Mix of sun and cloud. Possible trace of snow expected. Moderate northwest ridgetop wind, possibly strong at high elevations. Treeline temperature around -7 °C.

Thursday

Mix of sun and cloud. No new snow expected. Light to moderate southwest ridgetop wind. Treeline temperatures around -10 °C in the morning, rising to -5 °C through the day.

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.
  • Approach lee and cross-loaded slopes with caution.
  • Uncertainty is best managed through conservative terrain choices at this time.
  • Use caution above cliffs and terrain traps where even small avalanches may have severe consequences.

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.

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.