Avalanche Forecast
Issued: Dec 28th, 2021 3:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
JSmith,
Avalanche Canada
Recently formed storm slabs will be most reactive to human triggers in wind affected terrain.
A persistent slab problem has created a low likelihood, high consequence scenario that is best avoided through conservative terrain choices.
Summary
Confidence
Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.
Weather Forecast
TUESDAY NIGHT: Partly cloudy / Light north wind / Low of -24
WEDNESDAY: Sunny / Light north wind increasing to moderate in the afternoon / High of -17
THURSDAY: Mix of sun and cloud / Light to moderate northwest wind / High of -17
FRIDAY: Sunny / Light northeast wind / High of -17
Avalanche Summary
A rider triggered size 2.5 persistent slab avalanche involving several riders was reported near Nelson on Monday. The avalanche occurred on a southeast aspect at approximately 1900 m. It failed on the crust formed in early December. The treeline slope was heavily wind effected and the rider triggered the avalanche from a thin spot where the layer was only around 60 cm deep. There is a MIN report of the incident.
Additionally, several natural and human triggered storm slab avalanches up to size 2.5 were reported on all aspects and elevations on Monday. An example of a skier triggered storm slab near Rossland can be found in a MIN report HERE.
Snowpack Summary
Recent storm totals reached over 100 cm. Expect dry loose avalanches (sluffing) running far and fast in steep terrain. There is a lot of snow available for transport which will form fresh wind slabs when wind speeds increase to moderate.
The recent snow reportedly covered a thin freezing rain crust and a surface hoar interface, which has been responsible for recent storm slab avalanches. For now, we don't expect the new snow to bond well to the old interface.Â
A crust from early December is now 50-120 cm below the surface, and is found up to 2300 m. A layer of weak facets (sugary snow) has been reported above and below this crust, and is the layer of concern in our persistent avalanche problem.
The lower snowpack is composed of several early-season crusts. Snow depths at treeline average 150-300 cm.
Terrain and Travel
- Use small low consequence slopes to test the bond of the new snow.
- Pay attention to the wind, once it starts to blow fresh sensitive wind slabs are likely to form.
- Seek out wind sheltered terrain below treeline where you can avoid wind slabs and find great riding.
- Be aware of the potential for large avalanches due to the presence of a persistent slab.
- Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
Problems
Storm Slabs
The recent snow may become more reactive to human triggers as it settles into a more cohesive slab. Look for signs of instability: whumpfing, hollow sounds, shooting cracks, and recent avalanches.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
A persistent slab problem formed by a crust down 50-150 cm has created a low likelihood, high consequence scenario that is difficult to forecast. This layer is most likely to be triggered in windy areas where the depth of the snowpack is highly variable.
Avoid likely trigger spots such as steep, rocky or convex slopes with a shallow or thin to thick snowpack.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 29th, 2021 3:00PM
