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Avalanche Forecast

Archived

Dec 19th, 2019–Dec 20th, 2019

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

Regions

Glacier.

The Avalanche Hazard is rated Considerable for TODAY, but will increase to high TONIGHT and TOMORROW!

Weather Forecast

Cloudy with sunny periods and isolated flurries today, freezing levels will hover around 800m, and winds will be light to moderate from the South-South West. The Atmospheric River will bear down upon us later this afternoon, and last until Sunday morning. Depositing 9cm tonight, 30+ cm Friday, 30+cm Saturday at Tree-Line.

Snowpack Summary

60-70cm of new snow now buries the Dec 11 surface hoar layer. Previous new snow, and moderate winds built storm slabs at all elevations. The Nov 23rd surface hoar/crust/facet combo is down +/-120cm but has become increasingly stubborn in testing. Both of these interfaces are expected to wake up this weekend!

Avalanche Summary

On Tuesday and Tuesday evening we had a decent natural cycle to size 3, dusting up-tracks and the Highway. Limited new activity was observed yesterday. A natural cycle will start early tomorrow morning as the atmospheric river passes over Rogers Pass, rapidly loading start zones with new snow accompanied by strong wind and rising temperatures.

Confidence

Timing of incoming weather systems is uncertain

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.