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Avalanche Forecast

Archived

Mar 23rd, 2022–Mar 24th, 2022

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Northwest Coastal.

Human triggered avalanches are likely at upper elevations, while wet and crusty snow makes for difficult travel conditions down low. Stick to low consequence terrain.

Confidence

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

Weather Forecast

Wednesday night: Flurries around 5 cm. Moderate southwest wind. Alpine low around -8 °C. Freezing level dropping to valley bottom. 

Thursday: A mix of sun and cloud. Moderate southeast wind. Alpine high around -6 °C. Freezing level 1200 m.

Friday: Mostly cloudy. Moderate south wind. Alpine high around -5 °C. Freezing level 1200 m.

Saturday: Mostly cloudy. Light southeast wind. Alpine high around -5 °C. Freezing level 1100 m.

Avalanche Summary

Avalanche conditions were touchy on Wednesday. Skiers and machines remotely triggered storm slabs size 1.5-2.

A widespread natural avalanche cycle occurred on Tuesday. Storm slabs up to size 2 ran at upper elevations and loose wet to size 3 at lower elevations. Some of these avalanches stepped down to the persistent weak layer. 

Prior to the storm, reports of persistent slab avalanches were steadily coming in over the last week from northwest of Terrace. These avalanches were large to very large (size 2-3), failing on a weak layer buried 60-100 cm deep mostly on northeast facing slopes. These avalanches were easily triggered by riders and vehicles, some remotely or sympathetically, and propagating long distances.

Snowpack Summary

30-50 cm of recent snow has seen variable wind effect at upper elevations. Below 1500 m, new snow depths taper and the snow may sit over a wet or crusty upper snowpack.

A weak layer of surface hoar is now buried 70-120 cm deep. A thick rain crust from mid-February 130-200 cm deep caps a well consolidated lower snowpack.

Terrain and Travel

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Keep in mind that human triggering potential persists as natural avalanching tapers off.
  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent avalanches.
  • When a thick, melt-freeze surface crust is present, avalanche activity is unlikely.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.