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Avalanche Forecast

Archived

Mar 6th, 2022–Mar 7th, 2022

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.

Regions

South Columbia.

Settling storm snow is still sensitive to human triggers. Expect greater reactivity in freshly wind loaded features around rigelines.

Persistent weak layers continue to be reactive at treeline in the Southern Selkirks. Other areas are rated as moderate.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast. Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack.

Weather Forecast

A cold front approaches from the north overnight, bringing light snowfall and cold temperatures.

SUNDAY NIGHT: Increasing cloud with strong west/northwest winds. Freezing levels drop to valley bottom overnight. 

MONDAY: Cloudy with isolated flurries bringing up to 5 cm of snow to the northeast corner of the region. Winds ease to moderate from the northwest. Freezing levels rise to 1500 m, alpine high of-2. 

TUESDAY: A mix of sun and cloud with isolated flurries. Light northeast winds. Freezing levels at valley bottom. Alpine high of -5.

WEDNESDAY: Mostly clear with light northerly winds. Freezing levels at valley bottom. Alpine high of -10. 

Avalanche Summary

Storm slab activity continues to taper off, with recent reports indicating the impact of the spring sun on the snowpack. 

On Saturday, reactivity in the storm snow was limited to wind loaded areas and convex rolls, producing slab avalanches to size 2. Loose wet activity to size 2 was reported out of many steep sun affected terrain features. 

Over the past two weeks we have seen the buried weak layers of surface hoar and crust from mid February and mid January regularly produce large persistent slab avalanches. Activity has been concentrated in the Valhalla, Goat, and Kokanee Ranges typically on north through southeast facing slopes at treeline elevations.

  • Multiple size 2-3 avalanches were remotely triggered from ridgeline features on Friday and Saturday, up to 90cm deep. 
  • A natural size 2 was triggered by solar input in the Valhallas on Friday. 
  • On Friday snowmobile triggered size 2 occurred near Slocan. Read the MIN report here for full details. 
  • Operators in the Valhallas have noted whumpfing in treeline and low alpine features. This is a clear sign of instability and to consider conservative terrain choices. 

Snowpack Summary

Northwest winds will redistribute recent storm snow onto south and east facing slopes. Wind loaded pockets will build over a sun crust on south-facing slopes. A layer of surface hoar may be buried in wind-sheltered terrain features over 30-50cm of settling snow. 

Lower elevations have seen warm temperatures last week and have a melt freeze crust on the surface (below 1800 m).

The late February weak layer combination of crust, facets and surface hoar is buried up to 50cm deep, and has been reactive mostly on south facing slopes during periods of sun. There is some uncertainty about whether this interface will be reactive as temperatures drop.  

Buried weak layers sit 50-100 cm deep, from mid February and mid January. They both consist of surface hoar and/or melt-freeze crusts. Recent trends indicate these layers have been more reactive in southern Selkirks around the Valhalla, Kokanee, and Goat Ranges. Several natural and human triggered avalanches have been produced on these layers in the last 3 days. See the Avalanche Summary for full details.

Terrain and Travel

  • Don't be too cavalier with decision making, storm slabs may remain sensitive to human triggering.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.