Avalanche Forecast
Issued: Feb 22nd, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Deep Persistent Slabs and Wind Slabs.
JSmith,
Avalanche Canada
Small wind slabs may be more reactive than expected where they are sitting on top of a fragile layer of surface hoar.
Summary
Confidence
Weather Forecast
SATURDAY NIGHT: Few clouds, light southwest wind, alpine temperature -11 C, freezing level below valley bottom.
SUNDAY: 3-10 cm. snow, moderate southwest wind, alpine temperature -5 C, freezing level 1000 m
MONDAY: Mostly cloudy with possible flurries; 0-3 cm, light west wind, alpine temperature -6 C, freezing level 900 m.
TUESDAY: Mix of sun and cloud, light to moderate southwest wind, alpine temperature -6 C, freezing level 900 m.
Avalanche Summary
There have been a few sporadic large avalanches over the past week. Most recently, a large (size 3) deep persistent slab avalanche was remotely triggered last 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 a whumpf on a ridge that released a small wind slab on an east-facing alpine slope which then stepped down to the facets at the bottom of the snowpack. Another size 2.5 deep persistent slab avalanche was observed on a southwest aspect in steep and rocky alpine terrain near Golden on Thursday (see MIN report). Additionally, a large snowmobile triggered avalanche was reported on a convex roll at treeline in Quartz Creek on Wednesday (see MIN report). These isolated, but large avalanches suggest that the Purcells region is currrently in a low probability, high consequence scenario that requires careful snowpack and terrain evaluation.
Snowpack Summary
5 cm of new snow has buried a widespread layer of surface hoar (size 5-15 mm.). This layer exists on all aspects and elevations except for steep solar aspects where it was melted by sun and windward alpine slopes where the layer was flattened by wind before being buried. Surface hoar sitting on a thin sun crust may exist on lower angle solar aspects which is a particularly nasty combination. 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.
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Cornice failure may trigger large avalanches.
Problems
Deep Persistent Slabs
Weak snow at the bottom of the snowpack continues to pose a deep persistent slab avalanche problem. The most recent activity has been focused around the Golden area, but steep, rocky, shallow terrain throughout the region should be treated with caution. Avoid big alpine slopes that are threatened by cornices overhead.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Wind Slabs
Small wind slabs may be more reactive than expected where they are sitting on top of a fragile layer of surface hoar.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine.
Likelihood
Expected Size
Valid until: Feb 23rd, 2020 5:00PM
