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Avalanche Forecast

Archived

Feb 17th, 2019–Feb 18th, 2019

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

Regions

North Columbia.

Two persistent weak layers in the snowpack continue to be a concern. A cautious approach to backcountry travel is recommended.

Confidence

High -

Weather Forecast

SUNDAY NIGHT: Clear with cloudy periods, light northwest wind, alpine temperatures drop to -18 C.MONDAY: Mix of sun and cloud, moderate northwest wind, alpine high temperatures around -14 C.TUESDAY: Cloudy with some isolated flurries with up to 5 cm of snow, moderate northwest wind, alpine high temperatures around -12 C.WEDNESDAY: Mix of sun and cloud, light north wind, alpine high temperatures around -10 C.

Avalanche Summary

On Saturday, skiers triggered a few small (size 1) storm slabs and wind slabs as well as one larger (size 2) persistent slab avalanche. The persistent slab avalanche was triggered on a north aspect at 2100 m and failed on a 60 cm deep surface hoar layer. On Friday, a few size 1.5 persistent slab avalanches were were remotely triggered on north aspects at treeline, failing on 40-60 cm deep surface hoar layers. Some larger (size 2) persistent slab avalanches were triggered on the same layers just outside the region boundary. More persistent slab activity occurred earlier in the week, predominantly on northeast aspects between 1200 and 1900 m.

Snowpack Summary

10-15 cm of low density snow has been blown around by strong northerly winds, creating reverse-loading on some slopes. Two prominent weak layers have been responsible for a several dangerous avalanches in the past two weeks. The upper layer was buried at the end of January and lies approximately 40 cm below the surface. The deeper 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 potentially 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 be large (up to size 3). These weak layers are most prevalent at treeline and below, but may also be found in sheltered areas in the alpine.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.