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Avalanche Forecast

Archived

Mar 8th, 2021–Mar 10th, 2021

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

Regions

North Rockies.

 A mix of sun, cloud and wind will maintain wind slabs as the main concern. Deeper layers in shallow snowpack areas in eastern parts of the region are still a concern. 

Confidence

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

Monday Night: Mainly cloudy with clear periods, moderate west wind, alpine temperature -8 C, freezing level at valley bottom.

Tuesday: Mix of sun and cloud with increasing cloudiness late in the day leading to overnight flurries, moderate to strong west wind, alpine temperature -3 C, freezing level 1200 m.

Wednesday: Mix of sun and cloud, light west and northwest wind, alpine temperature -7 C, freezing level at valley bottom.

Thursday: Mainly cloudy with sunny breaks, moderate to strong west and west wind, alpine temperature -4 C, freezing level 500 m.

Avalanche Summary

We have not received recent reports of avalanche activity.

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

Snowpack Summary

Strong south to west winds in exposed areas have scoured some slopes and built windslabs on others. Freezing levels reached treeline last Thursday and Friday. It has cooled since so you will likely find a new snow on the surface or a crust treeline and below.

About a metre of snow covers a weak layer of facets buried mid February. Slightly deeper there is a 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

  • Be careful as you transition into wind affected terrain.
  • Avoid freshly wind loaded terrain features.
  • Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.

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.