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Avalanche Forecast

Archived

Jan 18th, 2021–Jan 19th, 2021

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

Regions

Northwest Inland.

A fast moving pulse of moisture and wind will quickly build reactive storm slabs.

Confidence

Moderate - Uncertainty is due to the track & intensity of the incoming weather system.

Weather Forecast

MONDAY NIGHT - Mainly cloudy / Strong southwest wind, gusting upwards of 100 km/h / alpine high temperature near -1 / freezing level rising up to 1200 m

TUESDAY - Snow starting late Monday, 10-20 cm / west wind, 60-90 km/h / alpine high temperature near -2 / freezing level 1100 m and dropping through the day

WEDNESDAY - Cloudy with sunny breaks / northeast wind, 20-30 km/h / alpine high temperature near -8 / freezing level valley bottom

THURSDAY - Cloudy with sunny breaks / southeast wind, 10-20 km/h / alpine high temperature near -8 / freezing level valley bottom

Avalanche Summary

A handful of wind slab avalanches to size 2 failing naturally were observed Sunday. Avalanches to size 2 were reported on more southwesterly to southeasterly aspects above 1200 m. Skiers easily cut size 1 pockets in loaded terrain.

A natural avalanche cycle occurred Thursday into Friday with storm and wind slab avalanches to size 2, with poor visibility likely limiting alpine observations. The strong winds reached below treelline elevations - reports of numerous wind slab avalanches observed in steep terrain with crowns 20-30 cm deep and up to 150 m wide.

Check out this MIN report here of a large persistent slab avalanche that likely occurred during the Thursday-Friday natural cycle.

Last Tuesday, a previous avalanche cycle occurred in the south of the region as slab avalanches up to size 2 failed naturally in wind loaded terrain. 

Just over a week ago, explosives triggered a few size 2 persistent slab avalanches near the southern boundary of the region (Jan 10). And explosive control work near Ningunsaw (just outside the region, on Jan 9) produced several wind slabs to size 2.5 and one size 3 deep persistent slab failing on weak facets near the base of the snowpack. As we continue to track this persistent weak layer, these are a reminder of the "low probability; high consequence" scenario that persistent slab problems often create.

Snowpack Summary

Ongoing flurries and incremental loading dropped 15-25 cm fresh snow in recent days. Gusty and variable winds have impacted loose snow and developed slabs in exposed areas. Warm temperatures have produced a crust up to 800 m and higher on solar aspects.

A weak layer of surface hoar, maybe be found under recent storm snow (now down 20-50 cm) at treeline and below treeline. In the south of the region, another weak layer of surface hoar that was buried around the New Year has been reported down 50-70 cm in sheltered areas.

The lower snowpack has two crusts with potentially weak, faceted snow around them. Reports from the Smithers area suggest the upper crust is 70-140 cm below the surface and has shown signs of being possible to trigger from shallow areas. The deeper crust is near the bottom of the snowpack and is most likely to trigger from steep, rocky slopes, with a shallow or thin to thick snowpack.

Terrain and Travel

  • Watch for changing conditions today, storm slabs may become increasingly reactive.
  • Wind slabs are most reactive during their formation.
  • Be especially cautious near rock outcroppings, on steep convexities and anywhere the snowpack feels thinner than average.
  • 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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

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.