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Avalanche Forecast

Archived

Dec 20th, 2022–Dec 21st, 2022

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

Regions

Lizard-Flathead, South Rockies, Flathead, Lizard, Bull, Elkford East, Elkford West.

Use extra caution at treeline where triggering a persistent slab avalanche is more likely. Make conservative decisions, even a small accident can have big consequences during periods of cold weather and short days.

Confidence

Moderate

Avalanche Summary

On Monday several natural storm slab avalanches up to size 2 were observed on northeast aspects in the alpine.

Persistent slab avalanche activity has continued to taper off but these layers will likely remain triggerable in specific terrain features.

Snowpack Summary

In the alpine moderate northwest winds have likely redistributed the recent low-density snow (up to 35 cm) and formed fresh wind slabs in immediate lee features. On steep solar slopes, these new wind slabs and fresh snow will be sitting on a thin sun crust. In more sheltered areas, the new snow covers surface hoar and facets.

Around 50cm overlies a layer of surface hoar at treeline and a thin crust on steep south facing slopes. This layer was formed in early December and is less widespread than the other layers of concern in the snowpack.

The mid-November layer consisting of facets and surface hoar is now buried around 80 cm deep. These depths will vary throughout our region with decreased depths in the northern areas.

The snowpack in the forecast region is quite variable and increasingly complex with snowpack depths at treeline varying from 100cm to 200cm.

Weather Summary

Tuesday Night

Flurries bringing up to 5cm of new snow with Moderate southwest winds shifting to light northwest by the morning. Low of -32 at 1800m.

Wednesday

Mostly sunny with no new snow expected. Light to moderate northeast winds and a high of -28 at 1800m.

Thursday

Mostly sunny with no new snow expected. Light variable winds and a high of -28 at 1800m.

Friday

Cloudy with trace amounts of new snow expected. Southwest winds increasing throughout the day. High of -25 at 1800m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Closely monitor how the new snow is bonding to the old surface.
  • Avoid open slopes and convex rolls at and below treeline where weak layers may be preserved.
  • In times of uncertainty conservative terrain choices are our best defense.

Problems

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.

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.