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Avalanche Forecast

Archived

Mar 6th, 2021–Mar 8th, 2021

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

Regions

North Rockies.

 Wind slabs are the main concern. Deeper layers in shallow snowpack areas in eastern parts of the region are still a concern and are trickier to manage. 

Confidence

Moderate - Uncertainty is due to extremely variable snowpack conditions reported through the region.

Weather Forecast

Saturday Night: Mainly cloudy with isolated flurries, accumulation 1-3 cm, moderate southwest wind, alpine temperature -5 C, freezing level at valley bottom.

Sunday: Mainly cloudy with scattered flurries, accumulation 1-5 cm, moderate to strong west and southwest wind, alpine temperature -4 C, freezing level 1200 m.

Monday: Mainly cloudy with scattered flurries, accumulation 1-5 cm, moderate southwest wind, alpine temperature -3 C, freezing level 1300 m.

Tuesday: Mix of sun and cloud, moderate to strong west wind, alpine temperature -3 C, freezing level 1300 m.

Avalanche Summary

The warm temperatures this week triggered loose wet avalanches on solar (south throug west) aspects. Strong winds triggered wind slabs naturally up to size 2 and explosive controlled avalanche (near Pine Pass) up to size 3. 

See this MIN post near Mc Bride on Friday which sums up recent avalanche observations nicely.

Snowpack Summary

Strong south to west winds in exposed areas have scoured some slopes and built windslabs on others. Freezing levels reached treeline Thursday and Friday with +3 C at Renshaw, +8 C in Kakwa on the east side of the divide. It has cooled slightly since so you will likely find a dusting of new snow on the surface or a crust treeline and below.

There was a range of accumulated new snow totals from last weekend: somewhere around 90 cm in Pine Pass (the deepest), down to 30 or 40 cm in Kakwa. The key point is there's recent loose snow at higher elevations available for wind transport. 

About a metre of snow covers a weak layer of facets (and potentially surface hoar) from mid February and a slightly deeper, widespread persistent weak layer from late January/early February that consists of surface hoar. It is most prevalent around treeline elevations, but likely reaches into the alpine and in openings below treeline too. These layers are both significantly shallower in the east of the region.

Terrain and Travel

  • Avoid freshly wind loaded terrain features.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
  • In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.

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.