Avalanche Canada ldreier, Avalanche Canada

South Coast Inland Avalanche Forecast

Jan 11th, 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.

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.

Summary

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

An icon showing Storm Slabs

Likelihood

Likely-Very Likely

Expected Size

1 - 2

Around 10 to 30 cm snow are expected by the end of the day on Sunday. The highest amounts are expected in the Coquihalla area. The snow will fall with moderate wind from various directions, changing from westerly wind overnight to northerly during the day. The storm on Friday delivered up to 20 cm of snow which was redistributed by moderate to strong southwest wind. 

Slabs will likely be more sensitive in lee terrain features in the alpine and around treeline. The new snow will hide slabs which were formed by the previous storm. This will make navigating around wind slabs more tricky.

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 12th, 2020 5:00PM