Avalanche Forecast
Issued: Dec 12th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Persistent Slabs.
ahanna,
Avalanche Canada
Wind slabs will be the main concern on Monday. Be on the lookout for stiff, drifted snow and signs of instability like shooting cracks as you enter wind-affected terrain.
Summary
Confidence
Weather Forecast
Sunday night: A trace of snow. Moderate southerly wind. Treeline temperatures around -8 C. Freezing level valley bottom.
Monday: Mostly cloudy with flurries up to 5 cm. Moderate southeast wind. Treeline temperatures around - C. Freezing level 600 m.
Tuesday: 5-10 cm of new snow. Light southwest wind. Treeline temperatures around -8 C. Freezing level valley bottom.
Wednesday: Mostly cloudy. Light southeast wind. Treeline temperatures around -10 C. Freezing level valley bottom.
Avalanche Summary
Wind slabs up to size 2 were reactive to ski cuts and explosives on Sunday. A limited natural avalanche cycle up to size 2.5 was reported to have run during the storm on Saturday. Noteworthy naturals include a size 3 on a northwest aspect in the Selkirks and a size 2 on an east aspect in the Monashees.
Reports from Wednesday and Thursday indicate an increase in persistent slab reactivity prior to burial by the current storm. There were several reports of natural size 2 avalanches in alpine terrain as well as several human triggered size 1 wind slabs around treeline. The most reactive slabs were on convex wind-affected slopes. Most avalanches were in the top 20-30 cm of snow.
Snowpack Summary
15-30 cm of recent snow has seen redistribution by strong wind at upper elevations.
The defining feature of the snowpack is a prominent and widespread crust that reaches as high as 2400 m in the alpine now sits 40-70 cm below the surface. In many places, overlying snow is well-bonded to the crust but in others, weak faceted grains have been observed growing above it around treeline. Snowpack models show the faceting process progressing quickly at this elevation, likely due to the amount of heat and moisture trapped by the crust. We will be closely monitoring this layer going forward. The snowpack structure is relatively simple beneath the crust, with treeline snow depths around 100-200 cm.
Terrain and Travel
- Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
- Approach lee and cross-loaded slopes with caution.
- Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
Problems
Wind Slabs
Small inputs of new snow will continue to feed wind slabs. As wind direction shifts southeast on Monday, watch for changes in loading patterns. Treat wind affected areas below treeline with caution.
Aspects: North, North East, East, South East, West, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
40-70 cm of snow sits over a weak layer on a thick crust. While only a handful of avalanches have been reported to have run on this layer, they have been large. Avalanches on this layer may be triggered by humans or vehicles from thin spots or by large loads like wind slab avalanches.
Aspects: All aspects.
Elevations: Treeline, Below Treeline.
Likelihood
Expected Size
Valid until: Dec 13th, 2021 4:00PM
