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Avalanche Forecast

Archived

Jan 10th, 2020–Jan 11th, 2020

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

Regions

South Coast Inland.

Moderate southerly wind formed new slabs in lee terrain features on Friday. Deeper weak layers might still be sensitive to human triggering. 

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

FRIDAY NIGHT: Cloudy with snowfall, accumulation 5 to 10 cm, light southwest wind, alpine temperature -6 C, freezing level at 700 m.

SATURDAY: Cloudy with flurries, up to 5 cm accumulation, light northwest wind, alpine temperature -9 C, freezing level at 800 m.

SUNDAY: Cloudy with snowfall, 5 to 10 cm accumulation, light southerly wind, alpine temperature -15 C, freezing level below valley bottom.

MONDAY: Cloudy with sunny periods, light westerly wind, alpine temperature -25 C, freezing level below valley bottom.

Avalanche Summary

On Thursday, a few explosive triggered storm slab avalanches up to size 2 were reported. One explosive triggered avalanche released on the mid November facet/crust layer.

On Wednesday, avalanches were triggered with explosives and ranged from size 1.5 to 2.5. One avalanche of size 3 released on a deeper weak layer in the snowpack and reached a depth of 130 cm. It was triggered by explosives. 

On Tuesday, several natural and skier triggered slab avalanches of size 1 were observed. One wet loose avalanche of size 2.5 was reported. 

On Monday, a natural avalanche cycle occurred during the peak of the storm with avalanches up to size 3.5. 

Snowpack Summary

The storm on Friday brought less snow than expected, snowfall amounts reached up to 15 cm. The snow from the previous storm is gaining strength while the triggering of deeper weak layers remain a concern.

Deeper in the snowpack:

  • The previous storm snow loaded a touchy weak layer of feathery surface hoar in sheltered areas above 1800 m. Areas such as Manning, Henning, Stoyoma, Duffey, and Hurley should be treated as suspect.
  • A persistent weak layer is present near the bottom of the snowpack in the northern half of the region (e.g., Duffey, Hurley). The weak layer of sugary faceted grains exists around a hard melt-freeze crust from mid-November. This is an indicative snowpack setup for large and destructive avalanches. The likelihood of human-triggered avalanches decreases as the layer gets deeper but the consequence of triggering it would be severe.
  • There are currently no concerns deeper in the snowpack near Coquihalla summit.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • If triggered, storm slabs in-motion may step down to deeper layers and result in very 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.