Avalanche Forecast
Issued: Mar 21st, 2022 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs, Wind Slabs and Cornices.
zryan,
Avalanche Canada
Avalanche danger will increase as temperatures rise throughout the day. There is uncertainty around how the snowpack will handle this warm-up.
Choose increasingly conservative terrain as temperatures rise.
Summary
Confidence
Moderate - Uncertainty is due to whether buried persistent weak layers become active, triggering avalanches, with the arrival of the forecast weather. Uncertainty is due to the fact that cornice falls are particularly difficult to forecast.
Weather Forecast
MONDAY NIGHT: Cloudy with light flurries. Light westerly winds. Freezing level around 1300 m.
TUESDAY: Mainly cloudy with light flurries. Light to moderate westerly winds. Freezing level rising to 2500 m and staying elevated for the overnight period.Â
WEDNESDAY: A Cloudy morning, clearing into the afternoon. Moderate to strong southwesterly winds. Freezing level around 2500 m.
THURSDAY: Mainly clear. Light northerly winds. Freezing level around 1500 m.Â
Avalanche Summary
There have been some notable human-triggered avalanches in Kootenay Pass and the Nelson area in the past week. These large slab avalanches (size 2), failed on either a buried sun crust on solar aspects or surface hoar on shaded aspects. This MIN report from an incident on Saturday near Whitewater is an example of this problem.Â
Several natural storm slabs occurred overnight on Saturday with heavy snowfall. A few human-triggered storm slabs occurred on Sunday throughout the region in the alpine and treeline (size 1-2).Â
On Friday, an operator south of Nelson reported a large slab avalanche, triggered by a helicopter landing initiating a cornice failure. This avalanche stepped down to a deeper weak layer in the upper snowpack, suggesting that these deeper layers are still possible to trigger with large loads.
Snowpack Summary
10 to 15 cm of recent snowfall overlies last week's 50 to 70 cm of denser, more settled snow. New snow depths taper significantly with elevation, with moist and crusty surfaces below 1800 m and on south aspects into the alpine.Â
Last week's snow is bonding poorly to underlying layers in some areas. In the Selkirks, especially north of Nelson, it appears this snow is bonding poorly to the underlying sun crusts on solar aspects and surface hoar on shaded aspects. In the Monashees, it appears this snow has formed a stronger bond to underlying crusts. Several other crust layers are found 50 to 100 cm deep, and the snow is mostly well bonded to these crusts.
Terrain and Travel
- The more the snowpack warms-up and weakens, the more conservative you`ll want to be with your terrain selection.
- Minimize overhead exposure; avalanches triggered by warming or cornice fall may be large and destructive.
- Be aware of the potential for large avalanches due to the presence of a persistent slab.
- Avoid steep slopes when air temperatures are warm, it is raining, or solar radiation is strong.
- Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
Problems
Persistent Slabs
Last week's 30 to 60 cm of storm snow has formed a persistent slab above weak layers in some areas. This is a concern where there is a poor bond to underlying sun crust layers on south-facing slopes and surface hoar crystals on north-facing slopes. This problem seems most pronounced in the Selkirks around Nelson and around Kootenay Pass. (read more in this blog).
Several other crust/facet layers exist in the upper 100 cm of the snowpack. Human-triggered avalanches on these layers are unlikely, but large triggers such as a cornice failure, or a smaller avalanche stepping down to these layers is possible. Be extra cautious during period of rapid loading, significant warming, or strong solar radiation.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Wind Slabs
10-25 cm of recent snowfall and westerly winds have formed wind slabs in lee features in the alpine and treeline.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Cornices
Cornices have grown significantly in the past two weeks. Warm temperatures may make cause cornices to become weak. Cornice failures are dangerous on their own, but also have the potential to trigger larger avalanches on the slopes below.
Give them a wide berth when travelling on ridge-lines and minimize overhead exposure to large cornices.
Aspects: North, North East, East, South East, South, North West.
Elevations: Alpine.
Likelihood
Expected Size
Valid until: Mar 22nd, 2022 4:00PM
