Avalanche Forecast
Issued: Dec 3rd, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Deep Persistent Slabs.
zryan,
Avalanche Canada
A facet/crust layer at the base of the snowpack has shown reactivity in a recent size 2.5 skier remote avalanche. Cold temperatures will decrease the reactivity of wind slabs, but if triggered wind slabs may step down to this deeper layer resulting in larger avalanches.
Summary
Confidence
Moderate - Uncertainty is due to the limited number of field observations. Uncertainty is due to the fact that deep persistent slabs are particularly difficult to forecast.
Weather Forecast
Friday overnight: A mix of sun and cloud with trace amounts of new snow. Light northwesterly winds and alpine temperatures around -20 C.Â
Saturday: Flurries with trace accumulation. Light to moderate northerly winds with alpine temperatures dropping to around -25 C.Â
Sunday: Mainly cloudy with flurries. Up to 2 cm of new snow accumulation. Moderate winds from the southwest increase to strong in the afternoon. Temperatures increase throughout the day, reaching -15 in the evening.
Monday: A cloudy day with strong southerly winds. 3-10 cm of new snow throughout the day with alpine temperatures rising to -5 C.Â
Avalanche Summary
On Tuesday, a size 2.5 skier-remote persistent slab was reported on the MIN (see report here). The avalanche was triggered from around 100m away, by a group of 5 riders on an east aspect at 1400m. The avalanche was suspected to have failed on an early-season facet/crust layer.Â
Lots of whumping and cracking have been reported across the region, which is most likely associated with an early-season shallow snowpack, wind slab formation, and a weak facet/crust layer at the base of the snowpack.Â
Thank you for the all informative and detailed Mountain Information Network (MIN) reports! Remember that it is still early season, and we look forward to hearing more this weekend.
Snowpack Summary
Northerly outflow winds may create reverse loading in the alpine and treeline. Due to varied wind directions in the past week, expect to find a mix of old and new wind slabs on all aspects alpine and treeline. Expect these wind slabs to be stiffening with a significant drop in temperatures overnight on Friday.Â
Snow depth at treeline is approximately 80-120 cm, depths in the alpine range from 100-160 cm.
A facet/crust layer can be found near the bottom of the snowpack. This layer has been reported as being reactive to human triggering in the past week, with a notable skier-remote avalanche on Tuesday.
Terrain and Travel
- Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
- If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
- Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
Problems
Wind Slabs
Last week's snowfall combined with consistent southerly winds created thick wind slabs in the alpine and treeline. Recent northerly winds may cause reverse loading, and create fresh wind slabs on southerly aspects. A significant drop in temperature in the past 24 hours will likely stiffen these wind slabs, but human triggering remains possible.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Deep Persistent Slabs
A persistent weak layer of facets over a crust can be found near the bottom of the snowpack. This layer has been reported as being reactive to human triggering in the last week. Little information is available about this weak layer, and as a result, careful snowpack evaluation will be necessary to manage it.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 4th, 2021 4:00PM
