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Avalanche Forecast

Archived

Dec 30th, 2020–Dec 31st, 2020

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

Regions

Lizard-Flathead.

The new snow may be easy for riders to trigger on Thursday, particularly in steep and committing terrain. The possibility also remains of triggering buried weak layers, where they exist.

Confidence

Moderate - Forecast precipitation (either snow or rain) amounts are uncertain.

Weather Forecast

WEDNESDAY NIGHT: Cloudy with snowfall, accumulation 5 to 10 cm, 30 km/h west wind, alpine temperature -7 C.

THURSDAY: Partly cloudy, 20 km/h southwest wind, alpine temperature -6 C.

FRIDAY: Cloudy with snowfall, accumulation 5 cm, 20 to 30 km/h southwest wind, alpine temperature -5 C.

SATURDAY: Cloudy with snowfall, accumulation 10 to 20 cm, 40 km/h southwest wind, alpine temperature -5 C.

Avalanche Summary

The 5 cm of new snow was reported as being easy to trigger on Wednesday. As this new snow accumulates overnight, the likelihood of triggering it will increase.

Snowpack Summary

Around 5 to 10 cm is expected to accumulate by Thursday morning. This snow may slide easily, particularly in steep and committing terrain. The slabs may be a bit thicker and touchy in lee terrain features near ridges due to northwest to southwest wind.

In the Lizard Range, a few reports indicate a potential weakness in the snow around 20 to 40 cm deep, potentially on sugary faceted grains around a melt-freeze crust up to an elevation of approximately 1800 m and hard surface above.

Around 50 to 100 cm deep, weak layers of feathery surface hoar and/or faceted grains overly a hard melt-freeze crust. This layer appears to be 

Terrain and Travel

  • Approach lee and cross-loaded slopes with caution.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.

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.