Avalanche Forecast

Archived

Dec 27th, 2022–Dec 28th, 2022

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural and human triggered avalanches likely.

Below Treeline

Natural avalanches possible, human triggered probable.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches possible, human triggered probable.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

Purcells, Dogtooth, East Purcell.

There is a Special Public Avalanche Warning in effect for this region. Learn more: avalanche.ca/spaw

The new storm snow overlies a layer of surface hoar that is very reactive. Utilize simple terrain and careful route finding if planning mountain travel.

Watch for wind effect in recent storm snow. Expect wind loading around ridgelines and in mid slope terrain features.

Deeper weak layers remain a concern for step down avalanches in wind loaded terrain.

Confidence

Moderate

Avalanche Summary

On Monday a widespread natural avalanche cycle occurred with numerous small to large ( size 1-2) avalanches occurring. These avalanche primarily failed on surface hoar that was buried in the middle of December as well on the persistent weak layer buried mid November.

An increase in avalanche activity was reported during Sunday. Explosive testing at two different operations triggered many avalanches, all within the previous storm snow on north aspect terrain in the alpine. These avalanches where small to large (size 1 and 2) . Crown depths ranged from 20 to 40 cm and ran from 50 m in length to 150 m.

Additionally, professional snowmobile operations reported remotely triggering 8 small (size 1) avalanches during travel . These avalanche were located on south aspect terrain at 1600 m elevation , depths were approx. 30 cm with run lengths every short 3 m.

Activity from Friday was limited to small loose dry avalanches in steep terrain features.

If you are headed into the backcountry please consider filling out a Mountain Information Network report.

Snowpack Summary

A period of warm and wet weather has moistened upper surfaces with rain reported up to the 2100m elevation.

Sustained light to moderate southwest winds have continued to move up to 20cm of storm snow, creating wind slabs on north and east facing terrain features. Wind slabs sit over hard wind affected surfaces, a layer of facets or surface hoar increasing reactivity.

The main concern is a layer of surface hoar, facets, or crusts buried 40 to 80 cm deep from mid November. Avalanche activity on this layer has tapered off but it could still be possible to trigger this layer in isolated terrain features near treeline. Triggering becomes more likely as temperatures rise.

Alpine snowpack distribution is variable, with depths ranging from 70 to 140 cm.

Weather Summary

Tuesday Night

Cloudy with light snowfall 1 to 4 cm. Moderate southwest winds 30 km/h. Freezing levels variable between 1000 and 1500 m. Alpine temperatures cooling to -5°C .

Wednesday

Cloudy with light snowfall 1 to 5 cm. Moderate southwest winds 40 km/h. Freezing levels remain around 700 m with alpine temperatures of -4°C.

Thursday

Mostly cloudy some mid day clearing expected, very light snowfall, trace amounts. Light southwest winds 15 km/h. Freezing levels remain below 500 m with alpine highs of -3°C.

Friday

Clearing with no precipitation forecast. Light southwest winds 15 km/h. Freezing levels at valley bottom with alpine highs of -12°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.
Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.

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.

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.