Avalanche Forecast
Regions: Purcells.
Moderate southwest winds may form fresh wind slabs in lee terrain features at upper elevations. Use caution as you transition into wind affected terrain.
Confidence
Moderate - Uncertainty is due to the limited number of field observations.
Weather Forecast
TUESDAY NIGHT - Cloudy with scattered flurries, up to 5 cm / southwest wind, 20-40 km/h / alpine low temperature near -8
WEDNESDAY - A mix of sun and cloud with isolated flurries / southwest wind, 15-30 km/h / alpine high temperature near -7Â
THURSDAY - Mainly cloudy with scattered flurries / west wind, 15-30 km/h / alpine high temperature near -6
FRIDAY - Mainly cloudy with scattered flurries, up to 5 cm / southwest wind, 20-40 km/h / alpine high temperature near -8
Avalanche Summary
Moderate southwest winds may form fresh windslabs that could be reactive to human triggers at upper elevations.
Avalanche control work produced a few small (size 1) storm slab and dry loose avalanches on Saturday and Sunday.
A MIN report from the Clamshell near Golden reported a natural size 2.5 avalanche on Wednesday. This avalanche appears to have run on a weak layer roughly 40 cm below the surface, which seems to be an isolated problem in this area.
Snowpack Summary
15-35 cm of snow overlies a rain crust found up to 2400 m in the south of the region and 1800 m in the north. In the north, the recent snow may sit over a weak layer of surface hoar or facets at elevations around treeline where this crust is not found. The recent snow may not be bonding well to these old surfaces. There have also been some reports of an isolated weak layer 40 cm below the surface around Golden.
The lower snowpack is characterized by a couple of crusts, the most notable is from a rain event in early November that is 50 to 100 cm deep. This crust is sitting near the base of the snowpack, surrounded by a weak layer of sugary facets. It is most likely to be reactive to human triggers or in a step-down from a smaller avalanche in shallow, rocky areas.
Terrain and Travel
- Investigate the bond of the recent snow
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
- In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.
Avalanche Problems
Wind Slabs
10-30 cm of soft surface snow may be blown into unstable slabs. In certain areas this snow may be poorly bonded to underlying layers of surface hoar and/or crusts. The problem is more likely found in northern parts of the region (e.g. Golden).
Aspects: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1.5
Deep Persistent Slabs
A facet/crust layer from early November sits near the base of the snowpack. This layer has shown signs of recent reactivity with explosive control in shallow rocky locations producing large avalanches. It is most likely to be triggered by humans in shallow, rocky areas or in a step-down from a smaller avalanche.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Unlikely
Expected Size: 2 - 3