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Avalanche Forecast

Archived

Jan 4th, 2021–Jan 5th, 2021

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

Regions

South Columbia.

Storm slabs will likely be reactive to human triggering, especially in wind loaded areas. Watch for signs of instability such as whumpfing, cracking and recent avalanches. 

Concern remains for persistent weak layers, which are best managed through conservative terrain choices. 

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

MONDAY NIGHT - Flurries, 10 cm / light to moderate west wind / alpine low temperature near -9 

TUESDAY - Mainly cloudy with a few flurries / light southwest wind becoming moderate south in the afternoon / alpine high temperature near -7 

WEDNESDAY - Mainly cloudy with a few flurries, around 5 cm / moderate southwest wind, easing in the afternoon / alpine high temperature near -6 / freezing level 1300 m

THURSDAY - A mix of sun and cloud / light northeast wind / alpine high temperature near -5 

Avalanche Summary

On Sunday, numerous natural, human and explosive triggered storm slab avalanches up to size 3.5 were reported in the region. 

On Saturday, numerous natural and human triggered storm slabs to size 1 at treeline and below were reported.

Recently formed storm slabs will be most reactive in wind affected terrain at treeline and above.

Snowpack Summary

10-20 cm of new snow brings recent storm snow totals to around 60-70 cm. Recent strong southwesterly winds have formed widespread storm slabs at all elevations.

Two persistent weak layers buried in early/mid Dec. are now 110-180 cm below the surface. The form and distribution of these layers are HIGHLY VARIABLE and have created conditions that can vary significantly from one valley to the next. The first layer has been primarily reported as small surface hoar. The next layer has been reported as a thin freezing rain crust, surface hoar, or thick rain crust depending on elevation and location. As a result, diligent investigation of the snowpack is required to get a handle on local conditions.

Terrain and Travel

  • Avoid freshly wind loaded terrain features.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • Uncertainty is best managed through conservative terrain choices at this time.

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.