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Avalanche Forecast

Archived

Jan 19th, 2021–Jan 20th, 2021

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

Regions

Lizard-Flathead.

Look for pockets of loose snow in sheltered terrain. Dig down and investigate deeper layers before committing to big features.

Confidence

Moderate - Confidence is due to a stable weather pattern with little change expected.

Weather Forecast

TUESDAY NIGHT- Cloudy with isolated flurries / Southwest wind, 25-45 km/h / Alpine low temperature near -10

WEDNESDAY - Cloudy with sunny breaks / Southwest wind, 20-50 km/h / Alpine high temperature near -7

THURSDAY - Sun and cloud / Northeast wind, 10-15 km/h / Alpine high temperature near -8

FRIDAY - Sunny / Northeast wind, 10 km/h / Alpine high temperature near -11

Avalanche Summary

Last week, there were several natural and persistent slab avalanches between size 2.5-3 reported in the region. Avalanche activity has slowed, and deeper persistent layers are trending towards dormancy. However keep in mind, these avalanches are reminders of the "low probability; high consequence" scenario that persistent slab problems often create. 

On Wednesday and Thursday (Jan 14-15), explosives triggered numerous avalanches up to size 2.5, including a size 2.5 persistent slab avalanche each day.

Overnight Tuesday and during the day Wednesday (Jan 12-13), a widespread natural avalanche cycle up to size 3 was reported, one of which was a size 2.5 persistent slab avalanche.

Snowpack Summary

A variety of wind affected surfaces covers upper tree line and alpine terrain. A polished crust is found up to 1800 m and higher on solar slopes. Soft pockets of redistributed snow may hide in sheltered areas.

A layers we have been tracking in the snowpack is a layer of weak faceted snow over a hard melt-freeze crust found around 90-200 cm down. Recent sporadic, large, naturally triggered avalanches have occurred on this layer on large alpine slopes and were triggered by either smaller wind slab avalanches, or cornice falls. This layer is trending towards dormancy, however the most likely place to find such conditions would be steep and rocky alpine start zones. The November crust is faceting near the ground. Dig down and investigate the deeper snowpack layers before committing to big terrain.

Terrain and Travel

  • Be careful as you transition into wind affected terrain.
  • Be alert to conditions that change with elevation, aspect and exposure to wind.
  • In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.