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Avalanche Forecast

Archived

Feb 11th, 2019–Feb 12th, 2019

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

Regions

North Columbia.

This region is currently the hotspot of human-triggered avalanche activity. Despite the cold, dry weather, dangerous avalanches continue to occur. It's a time to dial things back and stay conservative. Check out the Forecaster Blog here.

Confidence

High -

Weather Forecast

MONDAY NIGHT: Mostly dry with some flurries early Tuesday morning. TUESDAY: Flurries. Light easterly winds at 2000m, moderate southwesterly winds at 3000m. Alpine highs around -15C.WEDNESDAY: Dry, becoming sunny. Light southeasterly winds. Alpine highs around -12C.THURSDAY: A mix of sun and cloud. Flurries starting later on. Light easterly winds. Alpine highs around -12C.

Avalanche Summary

A number of significant avalanches have occurred on persistent weak layers in this region over the last several days, making it the hotspot for human-triggered avalanches at this time.On Sunday, a size 3 slab avalanche released at 1750 m on a south aspect when a sluff stepped down to the mid-January layer. Another avalanche was remote-triggered from 80 m away on an east aspect at around 1600 m.On Saturday, a snowmobiler died in a large (size 2) slab avalanche in the Bone Creek drainage (report here). It was triggered by the rider at 2100 m on a south aspect. The crown fracture varied from 15-100 cm deep, suggesting wind loading was a factor in the incident. Also on Saturday, a very large (size 3.5) natural avalanche released in a layer down 70 cm, apparently caused by icefall.On Friday, there were two skier-triggered avalanches reported, one of which was triggered remotely from 25 m away.In addition to the persistent slab avalanches, a number of wind slab avalanche were noted over the weekend, on all aspects at higher elevations.

Snowpack Summary

There are two prominent, touchy weak layers in the snowpack that have been responsible for a several dangerous avalanches, including one fatality in this region. The upper layer was buried at the end of January and lies approximately 40 cm below the surface. The lower one was buried mid-January and lies approximately 75 cm below the surface. Both comprise a mix of surface hoar and facets and may lie on top of a sun crust on southerly aspects. Both layers are highly reactive and in any given location, one or both could potentially exist in the snowpack. Wide propagation has been noted, meaning avalanches have the potential to go big (up to size 3). These weak layers are most prevalent at treeline and below treeline elevations, but may also be found in sheltered areas in the alpine.Strong northerly and easterly winds have created complicated patterns of wind-loaded snow. Many slopes are reverse-loaded or cross-loaded.Average snow depths are approximately 300 cm. Very sporadically, failures have occurred near the base of the snowpack in or close to this region. These releases have almost all been from high alpine areas, possibly triggered close to rocky features.

Problems

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.

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.