Avalanche Canada cgarritty, Avalanche Canada

Northwest Inland Avalanche Forecast

Jan 11th, 2020 4:00PM

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

Cold temperatures and strong winds are the story for Sunday. Expect danger to increase over the day as snow is redistributed into reactive new wind slabs. This is expected to occur in exposed areas at all elevations.

Summary

Confidence

High -

Weather Forecast

Saturday night: Possible light flurries followed by clearing. Light northwest winds shifting northeast and increasing.

Sunday: Sunny. Moderate to strong northeast winds. Alpine temperatures around -27.

Monday: Sunny. Light to moderate east winds. Alpine temperatures around -28.

Tuesday: Sunny. Moderate east winds. Alpine temperatures around -28

Avalanche Summary

Reports from the region are limited, however widespread avalanche cycles occurred over the past weekend and again on Friday as a result of rapid loading during each storm. A MIN report detailing activity on Friday describes numerous 30 cm-deep storm slabs releasing from 35+ degree slopes and reaching size 2.5 (large) in many parts of the region. 

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 activity was noted 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, wind-redistributed 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

About 30 cm of new snow accumulated in the region on Friday. The new snow 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. There is uncertainty about where this layer remains a problem, but reports of avalanche activity on these layers before the last storm suggest they may be active. The new load delivered by Friday's storm increased this potential.

Terrain and Travel

  • Avoid freshly wind loaded terrain features.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Approach steep open slopes at and below treeline cautiously, buried surface hoar may exist.

Problems

Wind Slabs

An icon showing Wind Slabs

Likelihood

Very Likely

Expected Size

1 - 2

New snow from Friday's storm may react as dry loose sluffs in sheltered areas, but deeper, more reactive slabs should be expected in wind-affected areas. Forecast winds are set to increase and shift to northeast, meaning slabs may be found on a wide range of aspects. Cold, dense air flowing out of valleys are expected to spread this problem to lower elevations.

Aspects:

East, South East, South, South West, West, North West.

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 12th, 2020 5:00PM