Avalanche Forecast

Archived

Dec 23rd, 2022–Dec 24th, 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 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.

Step back to conservative terrain as the storm slab problem gets trickier. 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

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

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.