Avalanche Canada cgarritty, Avalanche Canada

Northwest Coastal Avalanche Forecast

Jan 9th, 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.

The hits keep coming. Cool temperatures and heavy precipitation are expected to bring lots of low density snow to the region on Friday. Danger will increase over the day as slabs form with settlement and wind loading.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Thursday night: Cloudy with increasing flurries bringing 15-20 cm of new snow. Strong south winds.

Friday: Cloudy with continuing snowfall bringing 20-30 cm of new snow and new snow totals to 35-50 cm by end of day, easing overnight. Light to moderate southwest winds. Alpine high temperatures around -5.

Saturday: A mix of sun and cloud. Light southwest winds. Alpine high temperatures around -12.

Sunday: Mainly sunny. Moderate northeast winds. Alpine high temperatures around -24.

Avalanche Summary

Observations of natural avalanche activity in the region over the past few days showed evidence of storm slabs reaching size 2.5 (large) in the Shames area and the Skeena corridor during the recent storm.

Similar but more recent wind slabs were also reported, with this activity more pronounced in Bear Pass area where strong outflow winds were recently observed.

Looking forward, another round of snowfall through Friday is expected to build a widespread new storm slab problem to manage over the coming days.

Snowpack Summary

Up to 40 cm of new snow is expected to accumulate in the region by the end of the day on Friday, with the deepest accumulations focused near the coast. The new snow will mainly bury wind-affected surfaces at alpine and upper treeline elevations. It may cover a new layer of surface hoar at lower elevations and in sheltered areas or a thin sun crust on steeper south-facing slopes.

Below the new snow interface, 80-100 cm of recent storm snow, also wind affected, has been forming a strengthening bond with an underlying crust up to treeline and yet another array of wind affected surfaces at higher elevations.

Below these layers the snowpack is generally well consolidated. Two older layers of surface hoar are now buried 130-180 cm deep. The recent widespread natural storm slab avalanche cycle was a good test of these layers, and there have been no reports of avalanches stepping down to them.

Terrain and Travel

  • Storm slab size and sensitivity to triggering will likely increase through the day.
  • Use conservative route selection. Choose simple, low-angle, well-supported terrain with no overhead hazard.
  • Avoid freshly wind loaded terrain features.

Problems

Storm Slabs

An icon showing Storm Slabs

Likelihood

Very Likely

Expected Size

1 - 2

Another day of heavy snowfall is expected to layer a new storm slab problem over the region on Friday. The forecast calls for low density snow, which means sheltered new accumulations may react as dry loose sluffs until snow settles into a more cohesive slab. Deeper, more reactive slabs will form much more quickly in wind-affected areas.

Aspects:

All aspects.

Elevations:

All elevations.

Valid until: Jan 10th, 2020 5:00PM