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Avalanche Forecast

Archived

Feb 14th, 2020–Feb 15th, 2020

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

Regions

Purcells.

A weak frontal system crossing the region on Saturday afternoon will form fresh wind slabs. Be cautious on wind loaded slopes and large steep terrain features.

Confidence

Moderate - Uncertainty is due to unpredictable avalanche behavior.

Weather Forecast

FRIDAY NIGHT: Mostly cloudy with some light flurries and trace accumulations, moderate wind with strong gusts from the west, alpine temperatures drop to -10 C.

SATURDAY: Increasing cloud with afternoon flurries bringing 5-10 cm of new snow, moderate wind with strong gusts from the west, alpine high temperatures around -6 C.

SUNDAY: 5-10 cm of snow overnight then clearing in the afternoon, light wind from the northwest, alpine high temperatures around -6 C.

MONDAY: Mix of sun and cloud, light wind from the west, alpine high temperatures around -8 C.

Avalanche Summary

A few natural size 2 avalanches were reported on east facing wind-loaded slopes on Friday. A few small (size 1) wind slabs have been human triggered at treeline and alpine elevations over the past few days.

A large avalanche was reported at Quartz Creek on Wednesday. The avalanche was triggered by a snowmobile on a convex roll at treeline. The crown of the avalanche was 150 cm thick, but it is uncertain whether the avalanche was a thick wind slab or ran on a persistent weak layer. On Monday, two deep persistent avalanches (size 2.5 and 3) were triggered with explosives in the central part of the region, both running on north aspects in the alpine. These isolated large avalanches highlight the the importance of careful snowpack and terrain evaluation in the Purcells.

Snowpack Summary

20-50 cm of low density snow has fallen over the past week and has shown some reactivity at higher elevations where it has been redistributed it into wind slabs. This snow sits above a rain crust that extends up to 1600-1900 m. Sun crusts can be found near the surface on steep south-facing slopes. The middle of the snowpack is generally settled but the base of the snowpack contains basal facets. It remains possible to trigger these deep weak layers in shallow rocky start zones or from a heavy trigger such as a cornice fall. 

Terrain and Travel

  • Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
  • Conditions may have improved, but be mindful that deep instabilities are still present.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.

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.

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.