Avalanche Forecast
Issued: Dec 18th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs and Storm Slabs.
dsaly,
Avalanche Canada
Recent loose snow is forming slab properties over a weak layer of surface hoar. Scattered reports document increasing reactivity, expect to find an increasingly touchy slab with more snow and wind on the way.
Summary
Confidence
Weather Forecast
FRIDAY NIGHT- Snow, 10-20 cm / south-southwest wind, 45-70 km/h / alpine high temperature near -5 / Freezing level rising to 1200 m, weak inversion
SATURDAY - Flurries, 5-10 cm / southwest wind, 45-60 km/h / alpine high temperature near -6
SUNDAY - Snow, 10-20 cm / southwest wind, 20-40 km/h / alpine high temperature near -3 / Freezing level rising to 1300 m
MONDAY - Snow and flurries, 10-15 cm / northwest wind, 20-40 km/h / alpine high temperature near -10
Avalanche Summary
Snowmobilers remotely triggered a storm slab over surface hoar Wednesday near Allen Creek (MIN report). We have limited field observations from this region, however expect slabs to become increasingly reactive as fresh snow gains cohesion and bonds over a weak and touchy surface hoar layer.
Several large natural avalanches were reported last Friday at Chappel Creek (see this MIN report). These avalanches occurred on south aspects at treeline elevations. Based on the depth of these avalanches, they likely failed on recently buried surface hoar and/or sun crust layers.
Snowpack Summary
Incremental loading has stacked 30-60 cm (with the higher numbers surrounding Blue River) low density snow around the region. Southwest winds have built slabs in lee features at upper elevations.
A weak layer of surface hoar that was buried about a week ago is now down 40-60 cm. In many areas the weak layer exists as a crust, and in other areas, surface hoar. The bond at this interface is poor, slabs will become increasingly reactive as fresh snow gains cohesion and slab properties.
Near the base of the snowpack is a crust that was buried in early November. This crust likely has weak facets associated with it. There have been no recent avalanches reported on this layer, though it may be possible to trigger from shallow, rocky terrain.
Terrain and Travel
- Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
- Avoid freshly wind loaded terrain features.
- As the storm slab problem gets trickier, the easy solution is to choose more conservative terrain.
- Investigate the bond of the recent snow before committing to your line.
Problems
Persistent Slabs
Intermittent snow and flurries continue to stack up, recent and fresh snow sits on a weak layer of surface hoar down 20-40 cm. Expect this layer to be most reactive in wind loaded terrain.
Some areas near Blue River likely have up to 40-60 cm of new snow on this layer, and it will be most reactive in places like this.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Storm Slabs
A storm slab problem will develop as up 20 cm fresh snow falls by Saturday morning. Southwesterly winds will encourage slab development.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 19th, 2020 4:00PM
