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Avalanche Forecast

Archived

Feb 7th, 2017–Feb 8th, 2017

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

Regions

Little Yoho.

Wind and storm slabs were less touchy than anticipated on Monday. However, ice climbers still may want to avoid climbs with overhead hazard for a while yet.

Weather Forecast

Up to 25mm of precip is expected with warming temperatures starting Thursday late in the day. Accompanied by strong West wind, we expect these weather inputs to elevate the danger rating to HIGH on Friday.

Snowpack Summary

The past 3-day storm has deposited 10 cm in Field and 25 cm at higher elevations. Strong winds from the Yoho Blow have been ripping through the Kicking Horse Pass, but outside this area the winds have generally been light except at the higher elevations. Overall a weak snowpack exists, and with several weak layer buried deep in the snowpack.

Avalanche Summary

A few small avalanches up to size1.5 were triggered by explosives on Mt. Bosworth today during a control run. In general, forecasters observed the avalanches during the control run to be thin and sluggish with little mass. A recreational party reported remotely triggering a size 1 avalanche from 10m away at the Hector Glades near highway 93N.

Confidence

Timing, track, or intensity of incoming weather system is uncertain on Thursday

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.