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Avalanche Forecast

Archived

Dec 29th, 2019–Dec 30th, 2019

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

Regions

Northwest Inland.

Dangerous avalanche conditions will develop as new snow accumulates on Monday.

Confidence

Moderate - Uncertainty is due to limitations in the field data.

Weather Forecast

SUNDAY NIGHT: Cloudy with flurries starting early in the early hours of Monday morning, moderate wind from the southwest, alpine temperatures around -5 C.

MONDAY: Frontal system intensifies throughout the day with 15-30 cm of snow by the afternoon as snow level rises from valley bottom to 800 m in the evening, strong wind form the southwest, alpine high temperatures around -2 C.

TUESDAY: Storm continues Monday night with another 10-20 cm of snow above 1000 m (rain below) then clearing by Tuesday afternoon, strong wind from the west, alpine high temperatures around -2 C.

WEDNESDAY: Cloudy with scattered flurries and up to 5 cm of snow, light wind, alpine high temperatures around -5 C.

Avalanche Summary

The incoming storm will create unstable storm slabs and add stress to buried weak layers on Monday and Tuesday. A size 1.5 skier-triggered avalanche was reported on the MIN on Friday (see full report and photos here). The avalanche occurred on a convex north-facing slope at treeline and failed on a surface hoar layer 50 cm below the surface. This is the first avalanche reported in the region the past few days, but highlights a potential persistent slab problem that could produce larger avalanches on bigger terrain features.

Snowpack Summary

20-40 cm of new snow is expected between Monday morning into Monday night. Mild temperatures and strong wind will make this new snow form reactive slabs. Reports suggest there are two layers of surface hoar buried 25-50 cm below the surface. A skier triggered avalanche at Ashman and snowpack test results near Smithers suggest these layers have now become reactive (see these recent MIN reports). There is uncertainty about the distribution of this layer, but the sheltered slopes around treeline elevations are the most suspect for having preserved surface hoar.

Terrain and Travel

  • Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
  • Use ridges or ribs to avoid areas of wind loaded snow.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.

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.