Avalanche Canada ldreier, Avalanche Canada

South Coast Inland Avalanche Forecast

Jan 10th, 2020 4:00PM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is moderate. Known problems include Storm Slabs and Persistent Slabs.

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

Summary

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

An icon showing Storm Slabs

Likelihood

Possible-Likely

Expected Size

1 - 2

The storm on Friday brought less snow than expected with up to 15 cm during the day. The snow from the previous storm is gaining strength. Slabs will likely be more sensitive in lee terrain features in the alpine and around treeline, where the snow was transported with moderate southerly wind.

Aspects:

All aspects.

Elevations:

All elevations.

Persistent Slabs

An icon showing Persistent Slabs

Likelihood

Possible

Expected Size

2 - 3.5

Two layers that cause concern:

  • In many parts of the region, with the exception potentially being near Coquihalla summit, recent storm snow may overly a touchy surface hoar layer found around treeline elevations in sheltered areas. This layer has produced large avalanches that have propagated far.
  • In the north half of the region, a weak layer is buried near the bottom of the snowpack. This layer has been responsible for recent large, destructive avalanches.

The likelihood of humans triggering these layers remains elevated due to the recent load applied to them. Storm slab avalanches could step down to these layers.

Aspects:

All aspects.

Elevations:

Alpine, Treeline.

Valid until: Jan 11th, 2020 5:00PM