Avalanche Forecast
Issued: Mar 20th, 2023 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs, Deep Persistent Slabs and Persistent Slabs.
rbuhler,
Avalanche Canada
Wind slabs may still be reactive in exposed terrain at higher elevations.
Human triggering of the lingering persistent and deep persistent layers remains a concern and very large avalanches remain possible.
Summary
Confidence
Moderate
Avalanche Summary
On Sunday, several natural size 3 solar-triggered deep persistent slab avalanches were reported from rocky alpine features between 2200 and 2700 m over the weekend. A remotely triggered size 2 persistent slab avalanche was reported on a NW aspect at 2400 m which failed down 70 cm on facets and was triggered from 30 m away. A human-triggered size 2 wind slab avalanche also occurred on a SE aspect at 2400 m which was estimated to have failed down around 80 cm. A variety of solar-triggered loose wet avalanches up to size 1.5 were also observed from steep, rocky slopes.
On Saturday, a natural size 2 cornice failure was reported from a NW aspect in the alpine which did not trigger a slab on the slope below. This MIN post describes an older natural size 4 near Golden and a more recent natural size 3. This is a good reminder of the scale and destructive potential of avalanches which are still possible when the deep weak layer is triggered.
Snowpack Summary
The snow surface includes a sun crust on solar aspects, surface hoar up to 10 mm in shady and wind-sheltered areas, small facets on polar aspects, and wind-affected surfaces in exposed terrain. Until recently, the wind was blowing from the southwest but it has now switched to the northeast and therefore wind slabs could exist on all aspects in exposed terrain.
A weak layer buried around March 12 is now down around 20-40 cm and typically consists of wind-affected snow, facetted snow, and a thin sun crust.
The middle of the snowpack includes at least a couple of lingering persistent weak layers down 50-90 cm including surface hoar in wind-sheltered terrain and a sun crust on south aspects. Activity on these layers has tapered off but still remains a concern in isolated areas.
The lower snowpack is made up of a widespread layer of large, weak facets, and/or depth hoar crystals. This weak layer has been responsible for a number of recent very large, destructive avalanches and will likely continue to be a concern for the rest of the season.
Weather Summary
Monday Night
Clear, winds northeast 20-30 km/h, treeline low around -10 °C.
Tuesday
Sunny, winds northeast 10-20 km/h, freezing level reaching around 1800 m.
Wednesday
Sunny, winds northeast 15-25 km/h, freezing level reaching around 2000 m.
Thursday
A mix of sun and cloud, winds southwest 15-25 km/h, freezing level reaching around 1700 m.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Avoid slopes when the solar radiation is strong, especially if they have large cornices overhead.
- Recent wind has varied in direction so watch for wind slabs on all aspects.
- Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
- If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
Problems
Wind Slabs
The storm snow from last week had been redistributed by southwest winds forming wind slabs. The wind has recently shifted to the northeast and may be forming new slabs where there is still loose surface snow available for transportation. Wind slabs should currently be expected on all aspects in wind-exposed terrain.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Deep Persistent Slabs
The base of the snowpack remains very weak. Very large human-triggered avalanches are possible at treeline and above. Avoid thin, rocky start zones and shallow areas with variable snowpack depth where you are most likely to trigger this layer.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
Lingering weak layers from January and February exist at all elevations on a variety of aspects. On shaded slopes, these layers generally present as surface hoar, and on sun-exposed slopes, they present as facets and a crust. Be aware these layers can be remotely triggered (from a distance).
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Mar 21st, 2023 4:00PM
