Avalanche Forecast
Issued: Mar 20th, 2022 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Persistent Slabs.
zryan,
Avalanche Canada
Crusts on solar aspect are becoming more the norm. Dry snow will exist on the more shaded aspects but watch for wind slabs at higher elevations.
Danger ratings are a step higher in the western part of the region around the Bugaboos where concern for persistent slabs is greatest.
Summary
Confidence
Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.
Weather Forecast
SUNDAY NIGHT: Mainly cloudy, light flurries. Light to moderate westerly winds. Freezing level dropping to 500 m.
MONDAY: Mainly cloudy, isolated flurries. Light to moderate westerly winds. Freezing level rising to 1500 m in the afternoon.
TUESDAY: Partially cloudy. Light to moderate southwesterly winds. Freezing level rising to 2000 m in the afternoon.
WEDNESDAY: Mainly cloudy, isolated flurries. Light to moderate southwest winds. Freezing level rising to 1500 m in the afternoon.Â
Avalanche Summary
We have heightened concern about a developing persistent slab problem in some parts of the Purcells (read more in this blog).
Several notable human-triggered slab avalanches occurred last week, suggesting that the recent snow is bonding poorly to the underlying layers. These occurred on a range of aspects above 2000 m, with the most notable reactivity observed on south-facing aspects. Most slabs were small in the top 20 to 30 cm of snow (size 1), but one larger 70 cm thick slab was remotely triggered from below by a group of skiers (size 2). This avalanche occurred on a south aspect at 2250 m.
Snowpack Summary
Last week's 30-70 cm of settled storm snow has been redistributed by westerly winds into wind slabs in lee areas. Snow depths taper significantly with elevation, with moist and crusty surfaces below 1800 m and on south aspects into the alpine.
In some areas, last week's snow is well bonded to old crust layers, while in other areas the snow has settled into a reactive slab above weak layers around the crusts. At this point, it appears persistent slab problems could be developing in the deeper snowpack areas along the western side of the range, while the eastern side more likely has thinner wind slabs. The lower snowpack is generally well bonded.
Terrain and Travel
- Carefully evaluate steep lines for wind slabs.
- Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
- Be aware of the potential for large avalanches due to the presence of a persistent slab.
- Uncertainty is best managed through conservative terrain choices at this time.
- Cornice failure may trigger large avalanches.
Problems
Wind Slabs
Recent snowfall and westerly winds are expected to have formed wind slabs in lee features in the alpine and treeline.
Cornices have grown significantly in the past two weeks. Give them a wide berth when travelling on ridge-lines and minimize overhead exposure to large cornices, especially when the temperature is warm or solar radiation is strong.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
This is mainly a concern in the western part of the region that received greater snowfall amounts last week. 30 to 70 cm of settled storm snow has shown evidence of forming a persistent slab above weak layers. The most reactivity has been observed on south-facing aspects, with reports of a poor bond to underlying sun crust layers. Weak surface hoar crystals may also exist in isolated areas on north-facing slopes.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Mar 21st, 2022 4:00PM
