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Avalanche Forecast

Archived

Jan 5th, 2021–Jan 6th, 2021

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

Navigate around wind loaded slopes and keep in mind the potential for surprisingly large avalanches due to isolated weak layers.

Confidence

Moderate - Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack.

Weather Forecast

A weak front crosses the region on Wednesday then clearing weather into the weekend.

TUESDAY NIGHT: Cloudy, strong southwest wind, temperatures around -5 C.

WEDNESDAY: Scattered flurries throughout the day with 5-10 cm of snow, moderate southwest wind, temperatures around -3 C.

THURSDAY: Cloudy in the morning then clearing in the afternoon, light north wind, temperatures around -5 C.

FRIDAY: Sunny, light wind, temperatures around -5 C.

Avalanche Summary

A few small (size 1-1.5) storm and wind slab avalanches were reported on Monday and Tuesday. A natural cycle of larger (size 2-3) storm slab avalanches occurred over the weekend during a more intense storm. There was also persistent slab avalanche on Sunday that was remotely triggered in a north facing gully around 1350 m (see the photo here). The avalanche failed on a 50 cm deep surface hoar layer, and illustrates how the current persistent slab problem is lingering in isolated areas.

Snowpack Summary

Moderate snowfalls and strong southwest wind over the past few days has likely left hard surfaces and wind slabs in exposed terrain. Roughly 30-40 cm of recent snow is settling above a crust that extends up to 1900 m. The main feature we are monitoring in the snowpack is a layer of feathery surface hoar and/or faceted grains over a hard melt-freeze crust found 50 to 100 cm deep. Reports suggest this layer is strong and bonded in most terrain, but remains suspect in the isolated areas where it is preserved. Unfortunately we do not have a clear picture of where this isolated areas exist.

Terrain and Travel

  • Be carefull around freshly wind loaded features.
  • Choose slopes that are well supported and have limited consequence.
  • Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.

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.