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Avalanche Forecast

Archived

Dec 24th, 2022–Dec 25th, 2022

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

Regions

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

Recent snow and strong winds have built wind slabs at all elevations.

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 buried in early December.

The primary concern in the snowpack is the mid-November layer consisting of facets and surface hoar, buried around 80 cm deep. This layer could become more reactive as temperatures increase on Monday and Tuesday.

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

Weather Summary

Saturday Night

Mostly cloudy with 10-15 cm of snow. Strong westerly winds ease back to moderate. Freezing level below 500 m.

Sunday

Mostly cloudy with light flurries bringing trace amounts of new snow. Moderate westerly winds. Freezing levels around 500 m, high temperatures of -7°C.

Monday

Cloudy with 10-15 cm of mixed precipitation expected. Strong southwest winds return. Freezing levels rise, to around 1000 m with an above freezing layer likely from 1300 to nearly 2500 m in the south. High temperatures of +2°C.

Tuesday

Wet snow and rain continues overnight with another 15 mm forecast, while freezing levels rise to around 1800 m over the day.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Storm slab size and sensitivity to triggering will likely increase through the day.
  • Watch for fresh storm slabs building throughout the day.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.

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.