Avalanche Forecast
Issued: Dec 13th, 2022 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
Fresh wind slabs are expected to form throughout the day as northwesterly winds redistribute the surface snow into lee areas in the alpine and treeline.
Conservative terrain selection and good travel habits will be essential to manage the developing deep persistent slab problem.
Summary
Confidence
Avalanche Summary
On Monday near Pemberton, a skier-triggered persistent slab avalanche occurred on a northwest aspect in the alpine. The bed surface of this avalanche was reported as a crust with large surface hoar above. Interestingly, this avalanche triggered a size 2 in adjacent terrain, which failed on facets and depth hoar near the ground level. This avalanche is a sign pointing toward a developing deep persistent slab problem in this region.
Observations are limited this time of year. Keep posting your observations to the MIN; it helps strengthen our information gathering.
Snowpack Summary
In deeper zones at 1900 m the snowpack is around 100-130 cm, which is low for the middle of December, and it has a weak structure.
Surface: Boot top powder in deep areas. Same old crusts, facets, and rocks on wind-scoured slopes. Wind slab pockets lee of ridges.Upper-pack: Below the fresh snow is well-developed surface hoar in sheltered areas. The upper part of the snowpack is generally low density and faceting (aka weak).Mid-pack: maybe a crust or two, with a layer of soft facets above. This is likely the primary weak layer.Lower-pack: facets and depth hoar (aka not strong).
Weather Summary
Tuesday night
Clear periods with isolated flurries. Alpine temperatures drop to a low of -9 °C. Ridge wind northeast 10-25 km/h. Freezing level at valley bottom.
Wednesday
Sunny. Alpine temperatures reach a high of -4 °C. Ridge wind 25 km/h gusting to 50 km/h from the northwest. Freezing level at valley bottom.
ThursdaySunny with cloudy periods. Alpine temperatures reach a high of 1 °C. Ridge wind north 15 km/h gusting to 60 km/h. Freezing level rises to 1800 metres.
FridaySunny. Alpine temperatures reach a high of 3 °C. Ridge wind 25 km/h occasionally gusting to 50 km/h. Freezing level rises to 2500 metres.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
- Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
- The best and safest riding will be on slopes that have soft snow without any slab properties.
Problems
Wind Slabs
Northwesterly winds are expected to form fresh, reactive wind slabs in the alpine and treeline. Watch for pockets of wind slab on the lee side of ridges or ribs.
With the sugary, faceted, and weak snowpack wind slabs could step down to the bottom of the snowpack, resulting in larger than expected avalanches.
Aspects: North East, East, South East, South, South West, West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Deep Persistent Slabs
A slab is starting to form over the very weak basal facets. Whumpfing and cracking have been observed in many locations and human triggering should be considered possible on any steep slopes where a cohesive slab of snow is found.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 14th, 2022 4:00PM
