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Avalanche Forecast

Archived

Jan 1st, 2021–Jan 2nd, 2021

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

Regions

Lizard-Flathead.

A storm will start to build new slabs and load buried weak layers. Time to dial the terrain choices back and adopt a conservative mindset this weekend.

Confidence

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

Weather Forecast

FRIDAY NIGHT: Cloudy with snowfall, accumulation 10 to 15 cm, 40 km/h southwest wind, alpine temperature -5 C, freezing level rising to 1400 m.

SATURDAY: Cloudy with snowfall, accumulation 10 cm, 40 km/h southwest wind, alpine temperature -5 C, freezing level 1400 m.

SUNDAY: Cloudy with snowfall, accumulation 30 to 50 cm, 50 km/h southwest wind, alpine temperature -4 C, freezing level 1500 m.

MONDAY: Partly cloudy with afternoon snowfall, accumulation 5 cm, 20 km/h southwest wind, alpine temperature -5 C.

Avalanche Summary

Recently, a few small storm and wind slab avalanches were triggered by explosives out of steep northerly terrain at treeline and lower alpine elevations.

Avalanche activity is expected to increase over the weekend during the stormy period. Riders could trigger storm or wind slabs and there remains a possibility of triggering deeper weak layers, which would result in destructive avalanches.

Snowpack Summary

Upwards of 20 cm of snow is forecast to accumulate in the region by Saturday afternoon. The snow will be accompanied by a rise in freezing level and strong southwest wind. Storm slabs are expected to build in sheltered terrain and wind slabs in exposed terrain at higher elevations.

In the Lizard Range, a melt-freeze crust has been reported around 20 to 40 cm deep and up to an elevation of 1900 m. A few reports suggest that sugary faceted grains may exist around the crust but others indicate no weakness. 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

  • Watch for fresh storm slabs building throughout the day.
  • 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.