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Avalanche Forecast

Archived

Feb 18th, 2020–Feb 19th, 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.

Triggering large deep persistent slab avalanches remains a concern on steep rocky slopes at higher elevations, especially ones getting hit by the sun.

Confidence

High - The number, quality, or consistency of field observations is good, and supports our confidence.

Weather Forecast

TUESDAY NIGHT: Clear, light north wind, alpine temperatures drop to -18 C.

WEDNESDAY: Sunny, light north wind, alpine high temperatures around -6 C.

THURSDAY: Sunny, light southwest wind, alpine high temperatures around -6 C.

FRIDAY: Sunny, light southwest wind, alpine high temperatures around -6 C.

Avalanche Summary

Reports over the long weekend were primarily limited to a few small (size 1) wind slab avalanches, dry loose avalanches, and cornice falls. 

There have also been a few sporadic large avalanches over the past week. Most recently, a large (size 3) deep persistent slab avalanche was remotely triggered on Sunday just outside the forecast region near Mt. Seven. Photos in the Mountain Information Network report show this avalanche was initiated by a skier causing on whumpf on a ridge that triggered a smaller wind slab on an east-facing alpine slope that stepped down to the basal facets. Another 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

Sunny weather could weaken cornices and the upper snowpack on steep south-facing slopes. Surface conditions are a mix of low density snow in sheltered terrain, sun crusts on south-facing slopes, and isolated wind slabs at higher elevations. At lower elevations (below 1600-2000 m) 20-40 cm of snow sits above a hard rain crust. The middle of the snowpack is strong, but the base of the snowpack contains basal facets that have resulted in sporadic large deep persistent slab avalanches, especially in shallow rocky start zones. 

Terrain and Travel

  • Be mindful that deep instabilities are still present and have produced recent large avalanches.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
  • Minimize exposure to sun-exposed slopes when the solar radiation is strong.

Problems

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.