Avalanche Forecast
Issued: Dec 4th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Deep Persistent Slabs, Loose Wet and Wind Slabs.
JSmith,
Avalanche Canada
Above freezing temperatures up high over night and into the day Saturday will continue to stress the snowpack. Consecutive hot days are increasing the likelihood of triggering large avalanches on a crust near the bottom of the snowpack.
Summary
Confidence
Low - Uncertainty is due to the limited number of field observations.
Weather Forecast
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FRIDAY NIGHT: Clear / Light, southwest ridgetop wind / alpine low temperature 0 / Strong temperature inversion with above freezing air 2000-3500 m.
SATURDAY: Sunny / Moderate, south ridgetop wind / alpine high temperature +5 / Strong temperature inversion with above freezing air 2000-3500 m. dissipating in PM.
SUNDAY: Mix of sun and cloud / Light, west ridgetop wind / alpine high temperature -3 / Freezing level valley bottom.
MONDAY: Cloudy / Strong, southwest ridgetop wind / alpine high temperature -3 / Freezing level valley bottom.
Avalanche Summary
No recent avalanches reported on Thursday.
On Wednesday, numerous loose wet avalanches were reported from NE slopes above 2000 m. These avalanches were up to size 1.5 with no significant propagation.
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Snowpack Summary
Recent sun and warm air in the alpine likely had the greatest impact on the upper snowpack, showing signs of instability and promoting further slab development and cohesion. This may be most concerning where these slabs sit above an old thin crust (down 15 cm) on south aspects and feathery surface hoar crystals in wind-sheltered areas.Â
Northerly aspects will likely see fresh wind slab development at upper elevations on leeward slopes and melt-freeze conditions may exist on solar aspects at upper elevations. New surface hoar formation can be found mostly at treeline and below where it was protected from the warm temperatures, sunshine and wind.
Treeline snowpack depths sit around 50 to 80 cm in the south of the region.Â
Crusts from mid-and early-November are generally found 30 cm below the snow surface and 10 cm up from the ground at all elevations. While they are showing resistant planar results in snowpack tests, a lot of uncertainty still exists with limited observations.
Terrain and Travel
- Avoid exposure to steep, sun exposed slopes, especially when the solar radiation is strong.
- Back off slopes as the surface becomes moist or wet with rising temperatures.
- If triggered loose wet avalanches may step down to deeper layers resulting in larger avalanches.
- Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
- Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
Problems
Deep Persistent Slabs
A crust exists near the base of the snowpack. A lack of decisive data on this layer is keeping it on our radar for now. While it's been showing some results in snowpack tests in some areas, most reports describe an improving bond to the overlying snow. Potential for full depth avalanches may exist in areas where weak, sugary facets overly this crust, especially in areas of smooth ground cover such as scree slopes, grassy slopes, or rock slabs.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Loose Wet
If the sun pokes out and alpine temperatures are above freezing wet loose avalanches may occur.
Aspects: East, South East, South, South West, West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Wind Slabs
Recent wind from south to southwest has likely formed fresh wind slab at upper elevations in the immediate leeward side of slopes and terrain features.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 5th, 2020 4:00PM
