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Avalanche Forecast

Archived

Jan 14th, 2021–Jan 15th, 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 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, human triggered possible.

Regions

Lizard-Flathead.

Human triggered avalanches remain likely as strong winds are expected to form fresh slabs throughout the day. Look for low-angle, sheltered slopes for the best, and safest riding.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

THURSDAY NIGHT - Mainly clear / light to moderate west wind / alpine low temperature near -5 

FRIDAY - Sunny with cloudy periods / strong west wind / alpine high temperature near -4 

SATURDAY - A mix of sun and cloud / light to moderate west wind / alpine high temperature near -7 

SUNDAY - Mainly cloudy with sunny periods and isolated flurries / strong west wind / alpine high temperature near -5

Avalanche Summary

With strong west winds in the forecast and a lot of fresh snow available to blow around, storm and wind slabs are expected to be easy to trigger on Friday, especially in wind loaded areas.

On Thursday there were numerous reports of explosives triggered avalanches up to size 2.5, including one size 2.5 persistent slab avalanche.

There was a widespread natural avalanche cycle with avalanches up to size 3 reported on Tuesday night and during the day on Wednesday. There were also reports of numerous explosives triggered avalanches up to size 2.5, one of which was a persistent slab avalanche.

Over the past week, there have been several natural and persistent slab avalanches between size 2.5-3 reported in the region. These avalanches are continued reminders of the "low probability; high consequence" scenario that persistent slab problems often create. 

Snowpack Summary

The region received over 50 cm of new snow between Tuesday night and Wednesday afternoon.

Roughly 80-120 cm of snow is now sitting on a crust that extends up to 1900 m. In isolated areas below treeline, this recent snow may be sitting on a weak layer of surface hoar.

The main feature we are monitoring in the snowpack is a layer of weak faceted snow over a hard melt-freeze crust found around 120-200 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.

Terrain and Travel

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Avoid freshly wind loaded terrain features.
  • Minimize exposure to steep, sun exposed slopes, especially when the solar radiation is strong.
  • Storm slabs in motion may step down to deeper layers resulting in large 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.