Dashboard Regions Weather Stations Radar Alerts Glossary
Contact About
Log In

Register for an account and never miss a forecast again!

Register

Avalanche Forecast

Archived

Jan 8th, 2021–Jan 9th, 2021

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

Regions

Lizard-Flathead.

  

Sporadic large natural persistent slab avalanches have recently been reported in this region. This low likelihood, high consequence scenario is best avoided by choosing conservative terrain away from overhead hazard.

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

  

FRIDAY NIGHT: Partly cloudy / Light, southwest ridgetop wind / alpine low temperature -16 / Freezing level valley bottom.

SATURDAY: Mix of sun and cloud / Light, southwest ridgetop wind / alpine high temperature -8 / Freezing level valley bottom.

SUNDAY: Cloudy / Moderate, west ridgetop wind / alpine high temperature -7 / Freezing level valley bottom.

MONDAY: Cloudy / Strong, west ridgetop wind / alpine high temperature -5 / Freezing level 1200 m.

Avalanche Summary

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. Another reminder of the "low probability; high consequence" scenario that persistent slab problems often create. See MIN report HERE.

Several size 1.5 human triggered avalanches were reported on Wednesday in the top 30 cm of storm snow. Over the past few days there have been several natural and explosive triggered storm slab avalanches in the size 1.5-2.5 range, as moderate amounts of snow and wind each day have kept the avalanche danger elevated.

Last Sunday there was a remotely triggered persistent slab avalanche in a north facing gully at 1350 m (see the photo here). The avalanche failed on a 50 cm deep surface hoar layer. This layer has been reported in sheltered terrain below treeline.

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 100-150 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

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.

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.