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Avalanche Forecast

Archived

Jan 9th, 2022–Jan 10th, 2022

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

Regions

South Columbia.

Continually check snowpack conditions as you travel through terrain. Back off if you find dense, slabby snow, or signs of instability like shooting cracks. Avoid exposure to terrain traps, especially in steep features.

Confidence

High - The number, quality, or consistency of field observations is good, and supports our confidence.

Weather Forecast

SUNDAY NIGHT: Mostly clear. No new snow expected. Light southwest wind trending to strong at higher elevations. Treeline high around -7 C. Freezing level at valley bottom, with a possible temperature inversion pushing the temperature above 2000 m warmer than -5 C.

MONDAY: Mostly clear, with increasing cloud through the day. Possible trace of snow expected. Moderate southwest winds trending to strong at higher elevations. Freezing level rising to around 500 m. 

TUESDAY: Mostly cloudy. 0-5 cm of snow expected overnight, with another 2-5 cm through the day. Moderate to strong southwest wind trending to extreme at higher elevations. Possibly above 100 km/h. Freezing level rising to around 800 m.

WEDNESDAY: Overcast. 5-20 cm of snow expected overnight, with another 10-40 cm through the day. Moderate southwest wind trending to extreme at higher elevations. Freezing level rising to around 1300m.

Avalanche Summary

On Sunday, avalanche control with explosives in the north end of the region produced several storm slab avalanches, mostly small, some large. These avalanches occurred mostly on northeast aspects at treeline and in the alpine.

Friday through Saturday, numerous natural and rider triggered storm slab avalanches up to size 3 were reported by professional operations in the region. Avalanche control with explosives produced size 1.5 to 3.5 avalanches, mostly in the storm snow.

The persistent early December crust/facet layer has recently been active in this region. On Friday, three naturally triggered size 2-3 avalanches on this layer were reported in mountain ranges just west of the Columbia river. They were reported at treeline and above on south and east aspects. Some were known to be windslab avalanches that stepped down to this deeper, persistent layer in a thin, rocky area. 

Snowpack Summary

The region received 35 to 50 cm low-density snow and significant periods of strong southerly wind since the start of the storm Thursday. This new snow fell on a variety of surfaces, thin sun crust on solar aspects, isolated surface hoar at treeline on sheltered slopes, fresh wind slabs in lee alpine features at treeline and above or even previous storm snow (20-50 cm) from the last weekend's storm.

We're actively monitoring the early December crust. In some places, it's scoured and on the surface, while in wind-loaded terrain features it can be found as deep as 150 cm below the surface. It consists of faceted grains above a bulletproof crust formed by the Atmospheric Rivers of early December. Avalanches failing on this interface have the potential to be very large. 

Terrain and Travel

  • If you are increasing your exposure to avalanche terrain, do it gradually as you gather information.
  • Don't be too cavalier with decision making, storm slabs may remain sensitive to human triggering.
  • Be aware of the potential for loose avalanches in steep terrain where snow hasn't formed a slab.
  • Avoid terrain traps such as gullies and cliffs where the consequence of any avalanche could be serious.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.

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.