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Avalanche Forecast

Archived

Dec 31st, 2020–Jan 1st, 2021

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

Regions

Lizard-Flathead.

The recent snow may be easy to move, with the thickest deposits found in steep, lee terrain features.

Confidence

High -

Weather Forecast

THURSDAY NIGHT: Cloudy with snowfall, accumulation 2 to 5 cm, 30 km/h southwest wind, alpine temperature -6 C.

FRIDAY: Cloudy with snowfall, accumulation 5 cm, 30 km/h southwest wind, alpine temperature -5 C, freezing level rising to 1400 m.

SATURDAY: Cloudy with snowfall, accumulation 15 to 25 cm, 40 km/h southwest wind, alpine temperature -5 C, freezing level 1400 m.

SUNDAY: Cloudy with snowfall, accumulation 20 to 40 cm, 40 km/h southwest wind, alpine temperature -4 C, freezing level 1500 m.

Avalanche Summary

The recent snow was reported as being easy to trigger. A few small storm and wind slab avalanches were also triggered by explosives out of steep northerly terrain at treeline and lower alpine elevations.

Snowpack Summary

Around 10 to 20 cm of recent snow remains soft in sheltered terrain but may have been blown into small wind slabs in exposed terrain from northeast switching to southwest wind. This snow may continue to slide easily, particularly in steep and committing terrain.

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. It remains to be seen if this layer will become an avalanche problem.

Around 50 to 100 cm deep, weak layers of feathery surface hoar and/or faceted grains may overly a hard melt-freeze crust. These layer appears to be bonding in certain areas of the region but remain suspect, where they exist.

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.