Avalanche Canada shorton, Avalanche Canada

Purcells Avalanche Forecast

Jan 10th, 2020 5:00PM

Carefully evaluate the snow and terrain as there are multiple avalanche problems to navigate.

Summary

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

FRIDAY NIGHT: Cloudy with isolated flurries and up to 5 cm of snow, light wind from the southwest, alpine temperatures drop to -12 C.

SATURDAY: Cloudy with scattered flurries and 5-10 cm of snow, light wind from the southwest, alpine high temperatures around -10 C.

SUNDAY: Scattered flurries with 5-10 cm of snow, light wind from the south, alpine high temperatures around -12 C.

MONDAY: Flurries in the morning with 5-15 cm of snow then partly cloudy in the afternoon, light wind from the southwest, alpine high temperatures around -18 C.

Avalanche Summary

A midweek storm resulted in widespread avalanche activity with large and very large avalanches (size 2-3). Several of these avalanches ran on deep persistent weak layers in alpine terrain (above 2400 m), resulting in 80-200 cm thick slabs. Others ran on a buried layer of surface hoar from late December that can be anywhere from 30-100 cm deep (such as this MIN report that provides a helpful example terrain that is likely to harbor this problem).

Since the storm, additional large deep persistent slab avalanches have been triggered with explosives and smaller wind slab avalanches have been triggered naturally (up to size 2) and by humans (size 1).

Snowpack Summary

Low density snow continues to accumulate across the region. Open terrain at higher elevations may be affected by moderate wind from the southwest and have freshly formed wind slabs. Two mid-pack surface hoar layers from mid to late December are now buried 70-130 cm deep. Snowpack tests and avalanche activity give evidence to these weak layers' potential to produce large avalanches, especially on steep slopes in sheltered terrain. The base of the snowpack in the Purcells is much weaker than in an average season, and there are deeper weak layers down 120 to 200 cm. This weakness is widespread across all aspects and it consists of crust, facets and depth hoar. It remains possible to trigger these deep weak layers in areas where the snowpack is thin, rocky, or variable.

Terrain and Travel

  • Be especially cautious as you transition into wind affected terrain.
  • Use caution on large alpine slopes, especially around thin areas that may propagate to deeper instabilities.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.

Valid until: Jan 11th, 2020 5:00PM