Avalanche Forecast
Issued: Jan 7th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs, Persistent Slabs and Loose Wet.
JSmith,
Avalanche Canada
Sporadic large natural persistent slab avalanches have recently been reported in this region. This low likelihood, high consequence scenario is best avoided by choosing conservative terrain away from overhead hazard.
Summary
Confidence
Moderate - Uncertainty is due to the limited number of field observations. Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.
Weather Forecast
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THURSDAY NIGHT: Mostly clear / Light, southwest ridgetop wind / alpine low temperature -13 / Freezing level valley bottom.
FRIDAY: Mix of sun and cloud / Light, southwest ridgetop wind / alpine high temperature -5 / Freezing level valley bottom.
SATURDAY: Mix of sun and cloud / Light, southwest ridgetop wind / alpine high temperature -8 / Freezing level valley bottom.
SUNDAY: Cloudy with sunny periods / Moderate, northwest ridgetop wind / alpine high temperature -7 / Freezing level valley bottom.
Avalanche Summary
A couple large (size three) naturally triggered persistent slab avalanches were reported on large alpine features on Thursday. These avalanches were triggered by either smaller wind slabs in motion or cornice falls. Another reminder of the "low probability; high consequence" scenario that persistent slab problems often create.
Several size 1.5 human triggered avalanches were reported on Wednesday in the top 30 cm of storm snow. Over the past few days there have been several natural and explosive triggered storm slab avalanches in the size 1.5-2.5 range, as moderate amounts of snow and wind each day have kept the avalanche danger elevated.
On Sunday there was remotely triggered persistent slab avalanche in a north facing gully at 1350 m (see the photo here). The avalanche failed on a 50 cm deep surface hoar layer. This layer has been reported in sheltered terrain below treeline.
Snowpack Summary
Moderate snowfalls and strong southwest wind over the past few days has likely left hard surfaces and wind slabs in exposed terrain. Roughly 30-50 cm of recent snow is settling above a crust that extends up to 1900 m. The main feature we are monitoring in the snowpack is a layer of feathery surface hoar and/or faceted grains over a hard melt-freeze crust found 50 to 100 cm deep. Reports suggest this layer is strong and bonded in most terrain, but remains suspect in the isolated areas where it is preserved. Unfortunately, we do not yet have a clear picture of where these isolated areas exist.
Terrain and Travel
- Be carefull around freshly wind loaded features.
- Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.
- If triggered loose wet avalanches may step down to deeper layers resulting in larger avalanches.
- Avoid exposure to slopes that have cornices overhead.
Problems
Wind Slabs
Strong southwest wind and a series of moderate snowfalls over the past few days has likely left reactive slabs in steep leeward terrain.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
The snowpack across the region has some isolated areas where persistent weak layers linger, including surface hoar and/or facets above a crust 50 to 100 cm below the surface. This is a difficult problem to manage because it does not seem to exist in most terrain, but in the isolated places where it does exist it can produce large destructive avalanches.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Loose Wet
Small wet loose avalanches or cornice falls may trigger deeper weak layers, resulting in large avalanches.
Aspects: South East, South, South West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Jan 8th, 2021 4:00PM
