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Avalanche Forecast

Archived

Jan 29th, 2018–Jan 30th, 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 avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
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

South Columbia.

Heavy snowfall and rising temperatures will cause a widespread avalanche cycle. It's best to avoid all avalanche terrain, free from overhead hazard.

Confidence

Moderate - Intensity of incoming weather systems is uncertain

Weather Forecast

Tuesday: 5-15 cm snow Monday overnight into Tuesday, with another 10-15cm during the day. Moderate south-easterly winds. Alpine temperature near -8. Wednesday: Scattered flurries (5 cm snow possible). Moderate south-westerly winds. Alpine temperature near -8.Thursday: Scattered flurries (5-10cm snow). Light to moderate to strong south-westerly winds. Alpine temperature -7. More information can be found in the Mountain Weather Forecast.

Avalanche Summary

A widespread natural storm slab avalanche cycle to Size 3.5 was reported on Monday, at all elevations and aspects. Large avalanches were running even at low elevations. See here for a good example in a MIN report. 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. Expect natural avalanche activity to continue through Tuesday, with the potential for some surprisingly large avalanches given how many persistent weak layers exist in the snowpack.

Snowpack Summary

15-35 cm of storm snow fell Sunday into Monday and temperatures warmed up to -1 at tree line. The snow fell with strong south winds at times, producing wind slabs in lee features at tree line and alpine elevations and in open areas below tree line.The new snow sits on a complex snowpack and there are three active weak layers that professionals are monitoring:1) 70-110 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 tree line elevations and possibly higher. 2) Deeper in the snowpack, the early-January persistent weak layer is 100 to 140 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. 3) Another weak layer buried mid-December consisting of a facet/surface hoar/crust combination is buried 120 to 170 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.