Avalanche Canada cgarritty, Avalanche Canada

Northwest 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.

Seek out sheltered low density snow while it lasts, strong winds are in the forecast. Keep eyes open for signs of instability like shooting cracks or recent avalanches telling you the new snow has settled into a reactive slab.

Summary

Confidence

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

Friday night: Cloudy with isolated flurries bringing a final trace of new snow. Light winds shifting from southwest to northwest.

Saturday: Mainly cloudy with isolated flurries and a trace of new snow. Light northwest winds shifting northeast and increasing overnight. Alpine temperatures around dropping to -20 or lower by late afternoon.

Sunday: Sunny. Moderate northeast winds, becoming strong at ridgetop. Alpine temperatures around -28.

Monday: Sunny. Moderate east winds. Alpine temperatures around -30.

Avalanche Summary

Reports from the region are limited, however a widespread avalanche cycles are likely to have occurred over the past weekend and again on Friday as a result of rapid loading during each storm. Friday's activity is suspected to have been focused toward higher elevation, wind-exposed areas.

Before the last storm, reports of persistent slab avalanches associated with buried surface hoar were trickling in, from Ashman, Houston Telkwas, and the Howsons. They included natural and artificially triggered avalanches ranging in size from 1.5-3, and have occurred on all aspects, mainly at treeline. Loading from recent snowfall has increased the size and consequences of avalanches that may occur on these layers.

Looking forward, new snow from Friday's storm will remain our primary concern. Under forecast cool temperatures the new snow may continue to react to human triggers as dry loose sluffs. Greater danger should be expected in areas where winds have redistributed snow into deeper and more reactive slabs. 

Snowpack Summary

Up to 35 cm of new snow is expected to accumulate in the region by the end of the day on Friday. The new snow has mainly buried wind-affected surfaces at alpine and upper treeline elevations. It may cover a new layer of surface hoar at sheltered lower elevations or a thin sun crust on steeper south-facing slopes.

Below the new snow interface, 40-60 cm of older, wind-affected storm snow is expected to be forming a good bond with the interface below it.

A concerning pair of surface hoar layers are currently buried about 75-120 cm below the surface in sheltered areas around treeline. Reports of avalanche activity on these layers before the last storm suggest they may be active. The new load delivered by Friday's storm has increased this potential.

Terrain and Travel

  • Avoid freshly wind loaded terrain features.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.

Problems

Storm Slabs

An icon showing Storm Slabs

Likelihood

Likely

Expected Size

1 - 2

Friday's snowfall brought a new storm slab problem over the region on Friday. New snow may react as dry loose sluffs in sheltered areas, but deeper, more reactive slabs should be expected in wind-affected areas. 

Aspects:

All aspects.

Elevations:

All elevations.

Persistent Slabs

An icon showing Persistent Slabs

Likelihood

Possible

Expected Size

1.5 - 2.5

Two weak layers of surface hoar are now buried about 75-120 cm deep in parts of the region. There is uncertainty about both the distribution of these layers as well as how they have reacted to the recent load of storm snow. Human triggering one of these weak layers may be possible around steep, sheltered openings near treeline.

Aspects:

All aspects.

Elevations:

Treeline.

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