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Avalanche Forecast

Archived

Dec 16th, 2022–Dec 17th, 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 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, human triggered possible.

Regions

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

Be aware that if triggered, avalanches may step down to deeper layers resulting in large, destructive avalanches. Keep your terrain choices conservative and be prepared to back off quickly if you find signs of instability like whumpfing and shooting cracks.

Confidence

Moderate

Avalanche Summary

On Thursday Several size 2 natural avalanches were observed in treeline terrain in the Elkford area. These avalanches likely failed on the mid November surface hoar layer which is down around 40 in this area.

Last weekend, there were several alarming reports of large (size 2-3) persistent slab avalanches. They were remotely triggered by skiers or snowmobiles at treeline elevations. Check out these MIN reports here and here. A huge thank you to the groups who shared their observations to the Mountain Information Network!

Snowpack Summary

around 10cm of recent snow overlies a thin sun crust on steep south slopes and surface hoar and facets in sheltered terrain. Northwest winds will likely have redistributed snow onto south and east slopes and cross loaded others.

A well settled upper snowpack may overlie a layer of surface hoar formed in early December, now buried 30-50 cm deep. The mid November layer consisting of facets and surface hoar is now buried 70-90 cm deep. How ever both these layers can be found much shallower in the northern part of this forecast region. At the bottom of the snowpack, a thick crust sits on the ground.

At treeline, snowpack depths vary from 120 to 200 cm.

Weather Summary

Friday Night

Cloudy with the possibility of flurries bringing up to 5cm of new snow. Moderate to strong northwest ridge top winds shifting to west in the morning with a low of -14 at 1800m.

Saturday

Mostly cloudy with flurries bringing up to 10cm of new snow. Light to moderate westerly wind. High of -12 at 1800m.

Sunday

Mostly cloudy with flurries bringing up to 5cm of new snow. Moderate southwest wind. High of -18 at 1800m.

Monday

Mostly cloudy with light flurries bringing trace amounts of new snow. Moderate southwest winds and a high of -20 at 1800m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Pay attention to the wind, once it starts to blow fresh sensitive wind slabs are likely to form.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • 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

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.