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Avalanche Forecast

Archived

Jan 28th, 2018–Jan 29th, 2018

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

Regions

North Columbia.

Warm storm coming! Avoid all avalanche terrain during periods of heavy snowfall, including exposure to overhead hazard.

Confidence

Moderate - Intensity of incoming weather systems is uncertain

Weather Forecast

Monday: 15 cm snow Sunday overnight into Monday. 15-25 cm additional snow during the day. Moderate to strong south-westerly winds. Alpine temperature warming in the afternoon to near -2. Freezing level rising to 1200m in the afternoon. Tuesday: 5-15 cm snow. Moderate south-easterly winds. Alpine temperature near -5. Wednesday: Isolated flurries (up to 5cm possible). Moderate southerly winds. Alpine temperature near -5.More information can be found in the Mountain Weather Forecast.

Avalanche Summary

On Saturday a human-triggered Size 2.5 avalanche was reported near 2300m on a south west aspect in Glacier National Park. See the MIN report for incident details. Locally heavy snowfall in the Monashees on Saturday produced a widespread natural avalanche cycle in the afternoon. A widespread natural avalanche cycle is expected with Monday's storm, with the potential for some surprisingly large avalanches given how many persistent weak layers exist in the snowpack.

Snowpack Summary

The current snowpack is complex, with three active weak layers that we are monitoring. The recent storm snow fell with strong south winds, producing wind slabs in lee features at treeline and alpine elevations and in open areas below treeline.1) 60-90 cm of storm snow sits on a crust and/or surface hoar layer from mid-January. The crust is reportedly widespread, with the possible exception of high elevation north aspects. The mid-January surface hoar is 5 to 20 mm in size and was reported at treeline elevations and possibly higher. 2) Deeper in the snowpack, the early-January persistent weak layer is 90 to 120 cm below the surface. It is composed of surface hoar on sheltered slopes as well as sun crust on steep solar aspects and is found at all elevation bands. Snowpack tests show sudden fracture characters and signs of instability such as whumpfs, cracking and avalanches. 3) Another weak layer buried mid-December consisting of a facet/surface hoar/crust combination is buried 100 to 150 cm deep. It is most problematic at and below tree line.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.