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Avalanche Forecast

Archived

Dec 5th, 2022–Dec 6th, 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 unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

South Rockies, Bull, Crowsnest North, Crowsnest South, Elkford East, Elkford West.

Fresh, reactive wind slabs are expected to form throughout the day. Watch for signs of instability such as whumpfing, cracking, and recent avalanches.

Concern remains for the persistent weak layers near the base of the snowpack. A conservative approach to terrain and is advised.

Confidence

Low

Avalanche Summary

On Sunday, explosive control produced a large (size 2.5) wind slab avalanche on a southeast aspect in the alpine. This avalanche gouged down to the facetted lower snowpack in its track and as a result, entrained a large amount of mass.

On Saturday, a few, small (size 1) skier-triggered wind slabs occurred at treeline and below treeline.

Looking forward, we expect human-triggered wind slabs will remain possible, especially where new snow and wind are forming fresher, more reactive slabs. Consider the fact that these slabs have the potential to 'step down' to the facetted lower snowpack, resulting in larger avalanches.

We have very few eyes out there. If you do get out please consider reporting in the MIN.

Snowpack Summary

Overnight and throughout the day 5-10 cm of new is expected to be redistributed by westerly winds into fresh, reactive wind slabs in the alpine and treeline.

This snow overlies a heavily wind-affected surface in open areas. In the alpine, many slopes may have been stripped back to early-season layers or rock.

30-60cm of snow sits on top of a weak, sugary, faceted lower snowpack. Cold temperatures have weakened and faceted the snowpack as a whole. A rain crust sits near the ground.

Total snowpack depths at treeline elevations are 50-80 cm.

Weather Summary

Monday night

Cloudy with snowfall, up to 10 cm of accumulation expected. Westerly winds 30-60 km/h at ridgetop. Treeline temperatures drop to a low of -15 C.

Tuesday

Cloudy with snowfall, up to 5 cm of accumulation. Northwesterly winds 40-60 km/h at ridgetop. An alpine temperature inversion is possible, with valley bottom temperatures close to -20 C and alpine temperatures around -10 C.

Wednesday

A mix of sun and cloud with some lingering snow flurries. Westerly winds 20-40 km/h at ridgetop. Treeline temperatures reach a high of -10 C.

Thursday

Cloudy with snowfall, up to 5 cm of accumulation. Westerly winds 30-60 km/h at ridgetop. Treeline temperatures reach a high of -5 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.
  • Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger 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.