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Avalanche Forecast

Archived

Feb 16th, 2020–Feb 17th, 2020

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

Regions

Purcells.

With inviting sunny weather in the forecast for the next few days be mindful that triggering large deep persistent slab avalanches remains in concern on rocky alpine slopes.

Confidence

High - Confidence is due to a stable weather pattern; little change is expected for several days.

Weather Forecast

SUNDAY NIGHT: Partly cloudy, light northwest wind, alpine temperatures drop to -12 C.

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

TUESDAY: Mostly sunny, light wind from the northwest, alpine high temperatures around -8 C.

WEDNESDAY: Sunny, light northwest wind, alpine high temperatures around -5 C.

Avalanche Summary

Reports from Sunday were limited to a few small (size 1) wind slab and dry loose avalanches, and a few small cornice falls. Large sporadic avalanches have been reported every few days over the past weeks. Most recently a size 2.5 deep persistent slab avalanche was observed in steep rocky alpine terrain on a southwest slope near Golden on Thursday (see MIN report) and a large snowmobile triggered avalanche was reported on a convex roll at treeline at Quartz Creek on Wednesday (see MIN report). These isolated large avalanches highlight the importance of careful snowpack and terrain evaluation in the Purcells.

Snowpack Summary

10-20 cm of fresh snow and a total of 30-60 cm of snow from the past two weeks sits on the surface. This snow has shown some reactivity at higher elevations where it has been redistributed it into wind slabs. Sun crusts can be found near the surface on steep south-facing slopes and a hard rain crust can be felt beneath the snow at below treeline elevations. 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

  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
  • Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
  • Minimize exposure to sun-exposed slopes when the solar radiation is strong.

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.