Avalanche Forecast
Issued: Mar 19th, 2022 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs, Persistent Slabs and Loose Wet.
zryan,
Avalanche Canada
Avalanche danger will be highest during periods of strong solar radiation, affecting sun-exposed slopes and cornices.
Watch for wind slabs at upper elevations and adjust your travel plans according to the changing conditions of elevation, aspect, and time of day.
Summary
Confidence
Moderate - Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack. Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.
Weather Forecast
SATURDAY NIGHT: Snowing, 5-15 cm of accumulation. Moderate to strong westerly winds. Clearing in the early morning, 1500 m freezing level dropping to valley bottom with winds easing to light.
SUNDAY: Partially cloudy, cloud cover increasing in the afternoon. Light westerly winds. Freezing level rising to 1500 m.
MONDAY: Cloudy with light snowfall, up to 5 cm accumulation. Light to moderate westerly winds. Freezing level rising to 1500 m.
TUESDAY: Cloudy with light flurries. Moderate to strong westerly winds. Freezing level rising to 3000 m in the afternoon.
Avalanche Summary
Wind slabs are expected to be reactive to human-triggering in the alpine and exposed areas at treeline.
There have been some notable human-triggered avalanches in the Nelson area and in the South Columbia region in the past few days (read more in this blog). These have been larger storm slabs above weak layers, and we are uncertain whether these are signs of a developing persistent slab avalanche problem that could begin impacting northern and eastern parts of the Kootenay Boundary region.
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 20 cm of new snow overlies last week's 30 to 50 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
There is uncertainty about how well last week's snow is bonding to underlying layers. In the Selkirks, especially north of Nelson, it appears this snow could be bonding poorly to underlying crust and surface hoar layers. In the Monashees, it appears this snow has formed a stronger bond to underlying crusts. At this point, persistent slab problems could be developing in the deeper snowpack areas in the Selkirks. There are several other crust layers found 30 to 70 cm deep, and it appears the snow is mostly well bonded to these crusts.
Terrain and Travel
- Be aware of the potential for large avalanches due to the presence of a persistent slab.
- The more the snowpack warms-up and weakens, the more conservative you`ll want to be with your terrain selection.
- Cornices become weak with daytime heating or solar exposure.
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
Problems
Wind Slabs
10-25 cm of recent snowfall and southwest winds are expected to form reactive 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
30 to 60 cm of snow has shown evidence of forming a persistent slab above weak layers. There have been reports of a poor bond to underlying sun crust layers on south slopes and surface hoar crystals on north slopes, especially north and south of Nelson in the Selkirk Range. At this point, we are uncertain about how long this problem will take to heal and suggest a more conservative approach to terrain to handle this uncertainty.
Several other crust/facet layers exist in the upper 150 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: Alpine, Treeline.
Likelihood
Expected Size
Loose Wet
If the sun comes out on Sunday, daytime warming compounded by strong solar radiation may cause the surface snow on sun-affected slopes to loose cohesion rapidly and form wet loose avalanches out of steep terrain.
If triggered, wet loose avalanches have the potential to step down to deeper weak layers creating large avalanches.
Aspects: South East, South, South West, West.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Mar 20th, 2022 4:00PM
