Lizard Range and Flathead Avalanche Forecast

Issued: Jan 10th, 2021 4:00PM

Mon Jan 11th Current Conditions
Alpine Moderate Treeline Moderate Below Treeline Low
Tue Jan 12th 2 Day Outlook
Alpine Moderate Treeline Moderate Below Treeline Low
Wed Jan 13th 3 Day Outlook
Alpine Considerable Treeline Considerable Below Treeline Considerable

The alpine rating is moderate, the treeline rating is moderate, and the below treeline rating is low. Known problems include Wind Slabs and Persistent Slabs.

  

We continue to receive sporadic reports of large persistent slab avalanches failing on a deeply buried crust. Human triggering of this layer is most likely on steep, rocky terrain with a shallow or thin to thick snowpack.

Summary

Confidence

Moderate - Uncertainty is due to the limited number of field observations. Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

  

SUNDAY NIGHT: Cloudy / Light, west ridgetop wind / alpine low temperature -11 / Freezing level valley bottom.

MONDAY: Cloudy with isolated flurries; 0-3 cm. / Moderate, southwest ridgetop wind / alpine high temperature -6 / Freezing level 1200 m.

TUESDAY: Flurries; 3-5 cm, with another 15-25 cm. overnight / Extreme, southwest ridgetop wind / alpine high temperature -1 / Freezing level rising to 1800 m.

WEDNESDAY: Snow, 5-15 cm. / Moderate, west ridgetop wind / alpine high temperature -4 / Freezing level 1400 m.

Avalanche Summary

On Saturday, explosive testing near Fernie produced several large persistent slab avalanches up to size 2.5 failing on weak facets above a crust buried in early December.

A couple large (size three) naturally triggered persistent slab avalanches were reported on large alpine features on Thursday. These avalanches were triggered by either smaller wind slabs in motion or cornice falls. These are continued reminders of the "low probability; high consequence" scenario that persistent slab problems often create. See MIN reports HERE.

Snowpack Summary

Lingering wind slabs formed by recent snow and wind remain possible to human trigger in isolated areas. Roughly 30-50 cm of recent snow is settling above 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 facets(sugar snow) over a hard melt-freeze crust found around 150 cm down. Recent sporadic, large naturally triggered avalanches have occured on this layer on large alpine slopes and were triggered by either smaller wind slabs in motion or cornice falls.

Terrain and Travel

  • Be carefull around freshly wind loaded features.
  • Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Avoid exposure to slopes that have cornices overhead.

Problems

Wind Slabs

An icon showing Wind Slabs

Likelihood

Possible-Likely

Expected Size

1 - 1.5

Strong winds may form fresh wind slabs throughout the day on lee features at treeline and above. Wind slabs in motion may step-down to deeper weak layers resulting in large avalanches.

Aspects:

North, North East, East, South East, North West.

Elevations:

Alpine, Treeline.

Persistent Slabs

An icon showing Persistent Slabs

Likelihood

Possible

Expected Size

2 - 3

Wind slabs in motion and cornice falls have recently produced some very large avalanches failing on a crust down around 150 cm. Human triggering of this layer is most likely in steep, rocky slopes with a shallow or thin to thick snowpack.

Aspects:

All aspects.

Elevations:

Alpine, Treeline.

Valid until: Jan 11th, 2021 4:00PM