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Archived

Avalanche Forecast

Jan 18th, 2021–Jan 19th, 2021
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
3: Considerable
The avalanche danger rating below treeline will be considerable
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate

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.

Avalanche Problems

Storm Slabs

A pulse of moisture could dump up to 25 cm along with strong, gust wind. Expect increasingly reactive slabs to develop.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 1 - 2

Loose Wet

Freezing levels are expected to spike overnight and drop through Tuesday. Avoid steep slopes and terrain traps at low elevations where snow is wet.

Aspects: All aspects.

Elevations: Below Treeline.

Likelihood: Unlikely - Possible

Expected Size: 1 - 1.5

Persistent Slabs

Triggering large avalanches on weaknesses in the lower snowpack remains a possibility. In some areas the concern is weak snow around crusts 70-100 cm deep, while in others it is weak snow near the bottom of the snowpack. Human triggering of these layers are most likely in steep, rocky slopes with a shallow or thin to thick snowpack.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Unlikely

Expected Size: 2 - 3