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Avalanche Forecast

Archived

Jan 11th, 2020–Jan 12th, 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 possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

South Coast Inland.

Up to 30 cm snow are expected by the end of the day on Sunday. Highest amounts are forecast for the Coquihalla area. The avalanche danger will increase throughout the day with continuing snowfall and wind affect.

Confidence

Moderate - Forecast snowfall amounts are uncertain. Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

SATURDAY NIGHT: Cloudy with snowfall, accumulation up to 10 cm, light to moderate westerly wind, alpine temperature -10 C, freezing level at valley bottom.

SUNDAY: Mostly cloudy with snowfall, 5 to 20 cm accumulation with highest amounts in the Coquihalla area, light to moderate northerly wind, alpine temperature -15 C, freezing level below valley bottom.

MONDAY: Cloudy with sunny periods, light westerly wind, alpine temperature -22 C, freezing level below valley bottom.

TUESDAY: Mix of sun and cloud with isolated flurries, light to moderate southwest wind, alpine temperature -25 C, freezing level below valley bottom.

Avalanche Summary

No new avalanches were reported on Friday.

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. 

Snowpack Summary

The storm of the past days delivered up to 20 cm with moderate to strong southwest wind. The snow formed slabs in lee terrain features in the alpine and around treeline. 

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.
  • Storm slab size and sensitivity to triggering will likely increase through the day.

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.