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Avalanche Forecast

Archived

Dec 23rd, 2022–Dec 24th, 2022

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

Watch for wind loaded features as you move through terrain. Strong winds and snow are expected Saturday afternoon.

A buried surface hoar layer may increase reactivity, and small avalanches may step down to deeper weak layers.

Confidence

Moderate

Avalanche Summary

On Thursday loose dry avalanches to size 2 were reported in steep terrain features.

On Tuesday explosive control produced a few small avalanches, up to size one.

A natural size 2.5 persistent slab avalanche was reported, thought to have occurred on Tuesday. This avalanche occurred on a northeast aspect, 2000 m on a reloaded bed surface.

Snowpack Summary

New snow accumulates over the day, redistributed into larger deposits in east and north facing terrain. Slabs form over facets, surface hoar or a crust and may not bond well.

Around 50cm deep a layer of surface hoar at treeline and a thin crust on steep south facing slopes exists. 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.

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

Weather Summary

Friday Night

Cloudy with 5 cm of snow expected. Moderate westerly winds. Freezing levels below valley bottom.

Saturday

Mostly cloudy with around up to 15cm of new snow expected late afternoon. Strong to extreme southwest winds and a high of -16°C

Sunday

5-10 cm possible overnight. Mostly cloudy with light flurries bringing trace amounts of new snow. Moderate westerly winds. Freezing levels around 500 m, high temperatures of -10°C.

Monday

Cloudy with 5 cm of snow expected. Strong southwest winds return. Freezing levels rise, to around 1000 m with an above freezing layer possible at 2000 m. High temperatures of 0°C.

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.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.

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.