Avalanche Forecast

Issued: Jan 7th, 2020 4:00PM

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

Avalanche Canada mconlan, Avalanche Canada

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Storm slabs may remain touchy and could step down to deeper weak layers in parts of the region. Around Coquihalla where deeper weak layers aren't present, the danger may be Considerable. Nonetheless, the snowpack will need time to stabilize with all the recent snowfall.

Summary

Confidence

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

Weather Forecast

TUESDAY NIGHT: Cloudy with snowfall, accumulation 5 cm in the north of the region and 15 to 30 cm in the south of the region, moderate southwest wind, alpine temperature -5 C, freezing level 1200 m.

WEDNESDAY: Clear skies in the north of the region and light snowfall in the south of the region, accumulation 2 to 5 cm, light northwest wind, alpine temperature -11 C, freezing level below valley bottom.

THURSDAY: Clear skies, light northwest wind, alpine temperature -11 C, freezing level below valley bottom.

FRIDAY: Cloudy with snowfall, accumulation 5 to 10 cm, moderate to strong southwest wind, alpine temperature -9 C, freezing level below valley bottom.

Avalanche Summary

It is possible that a natural avalanche cycle occurred on Monday during the peak of the storm. Although naturally triggered avalanche activity is expected to decrease into Wednesday, human-triggered avalanches will remain likely to very likely.

Snowpack Summary

Around 20 to 30 cm of snow accumulated in the north of the region and 40 to 60 cm in the south of the region. Below around 1500 m, most of this fell as rain. The snow fell with strong southwest wind, likely forming the deepest and touchiest slabs in lee terrain features. 

Deeper in the snowpack:

  • The 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 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 deeper concerns near Coquihalla summit.

Terrain and Travel

  • Travel in alpine terrain is not recommended.
  • Don't let the desire for deep powder pull you into high consequence terrain.
  • 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

Around 20 to 30 cm of snow fell in the north of the region and 40 to 60 cm in the south of the region. The snow has formed touchy storm slabs, particularly in exposed terrain features, as the snow fell with strong southwest wind. These slabs may remain touchy to human traffic on Wednesday. It would be wise to stick to non-avalanche terrain at higher elevations until the snowpack stabilizes. Assess the bond of the recent snow before committing to avalanche terrain and travel conservatively.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 2.5

Persistent Slabs

An icon showing Persistent Slabs

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.

Likelihood

Possible - Likely

Expected Size

2 - 3.5

Valid until: Jan 8th, 2020 5:00PM