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Avalanche Forecast

Archived

Dec 18th, 2018–Dec 19th, 2018

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

Regions

Glacier.

Avalanche activity is expected to increase as the storm snow settles into a cohesive slab. Human triggering is likely. Stay in conservative terrain until the storm tappers off in a few days.

Weather Forecast

Another 10-15cm of snow forecasted for the day with an alpine high of -4, winds 30-55kph from the SW and a freezing level rising to 1600m (watch for tree bombs at low elevations). A forecasted 10cm on Wednesday and 30cm on Thursday with moderate - strong winds.

Snowpack Summary

15cm in the past 24hrs accompanied by moderate winds and near zero temps is building a storm slab and buries old wind slab in the Alpine. The Dec 9 surface hoar/facet persistent weak layer is buried 70-100cm and producing large 'whumphs' and sudden planar test results. The November 21st surface hoar/facet persistent weak layer is down 120-160cm.

Avalanche Summary

Several avalanches size 2 to 3 were observed along the highway corridor and several size 1.5 - 2 naturals reported from backcountry users yesterday. Large settlements on the Dec 9 layer are producing 'whumphs' that have traveled for over 100m in open terrain and seem most prevalent at tree line. Limited alpine observations due to poor visibility.

Confidence

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.