Avalanche Forecast
Issued: Mar 21st, 2023 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Deep Persistent Slabs, Wind Slabs and Persistent Slabs.
zryan,
Avalanche Canada
Strong solar radiation has initiated several large deep persistent slabs in the past few days. Start and finish your day early and plan to be well away from sun exposed slopes and overhead hazard before the warmest part of the day.
Human-triggering large slab avalanches remains possible in steep, rocky, and/or wind-affected terrain.
Summary
Confidence
Moderate
Avalanche Summary
Strong solar radiation in the past few days has triggered several natural size 3 deep persistent slabs, mainly on south aspects. These avalanches were reported from rocky alpine and treeline features between 1900 and 2700 m. A variety of solar-triggered loose wet avalanches up to size 1.5 were also observed from steep, rocky slopes.
On Sunday, 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.
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 daily melt-freeze cycle on solar aspects, surface hoar up to 10 mm in shady and wind-sheltered areas, faceting snow on polar aspects, and wind-affected surfaces 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
Tuesday night
Clear. Alpine temperatures reach a low of -4 °C. Light variable ridge wind. Freezing level at valley bottom.
Wednesday
Sunny. Alpine temperatures reach a high of -2 °C. Light variable ridge wind. Freezing level rises to 2000 metres.
Thursday
Sunny with cloudy periods. Alpine temperatures reach a high of -3 °C. Ridge wind 10 to 30 km/h from the southwest. Freezing level rises to 1800 metres.
Friday
A mix of sun and cloud with isolated flurries. Alpine temperatures reach a high of -5 °C. Ridge wind light from the southwest. Freezing level rises to 1000 metres.
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
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. Give careful consideration to the slopes overhead as large avalanches may run well into the runout zone or into lower-angle terrain.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Wind Slabs
Lingering wind slabs may still be reactive at higher elevations. Winds have recently shifted directions so wind slabs should be expected on all aspects in exposed terrain.
Aspects: All aspects.
Elevations: Alpine.
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 or facets, 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 22nd, 2023 4:00PM
