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Avalanche Forecast

Archived

Feb 17th, 2020–Feb 18th, 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.

Sunny weather is on the way. Remain cautious of large steep slopes at higher elevations, especially ones getting hit by the sun.

Confidence

Moderate - Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack.

Weather Forecast

MONDAY NIGHT: Clear with a few clouds, moderate north wind, alpine temperatures drop to -12 C.

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

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

THURSDAY: Sunny, light southwest wind, alpine high temperatures around -5 C.

Avalanche Summary

Preliminary reports from Monday suggest there was limited new avalanche activity. On Sunday a few small (size 1) wind slab avalanches, dry loose avalanches, and cornice falls were reported.

A few large sporadic avalanches have been reported over the past two 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 30-50 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.