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Avalanche Forecast

Archived

Feb 6th, 2021–Feb 7th, 2021

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

Regions

Northwest Inland.

Persistent slab avalanches can be difficult to predict, so a conservative approach is recommended. 

Storm slabs may still be easy to trigger, especially in wind loaded areas. Watch for a change in wind loading patterns with northerly winds.

Confidence

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

SATURDAY NIGHT - Mainly cloudy with isolated flurries / moderate northwest wind / alpine low temperature near -17 

SUNDAY - Sunny with cloudy periods / moderate to strong northwest wind / alpine high temperature near -16

MONDAY - A mix of sun and cloud / light southeast wind / alpine high temperature near -20

TUESDAY - A mix of sun and cloud / light east wind / alpine high temperature near -26

Avalanche Summary

There have been no new avalanches reported in the region for a few days, however, observations are limited. If you get out this weekend, please consider sharing your observations on the Mountain Information Network!

On Thursday a MIN report from the Seaton South Ridge about a size 1 wind slab on a north aspect at treeline. The report said that the bed surface had a few cm's of soft snow, possibly surface hoar, above a somewhat icy crust. The slab was small but ran fast on the bed surface. 

Once the new low-density storm snow becomes more consolidated and forms a slab, the likelihood of avalanches may increase.

 

Snowpack Summary

25-50 cm of recent, low-density storm snow from the past week sits on a persistent weak layer. This layer consists of surface hoar in locations sheltered from the wind at all elevations, facets, and stiff wind affected snow. On solar aspects, a buried sun crust can be found and a thick crust exists near the surface below 1000 m. 

The lower snowpack has two decomposing crust layers. The upper crust is 70-140 cm deep and continues to show occasional hard, sudden results in snow pits. 

The deeper crust at the bottom of the snowpack is more prevalent in shallow snowpack ranges. These deep persistent layers seem to be dormant under the current conditions, but shallow rocky slopes should still be carefully assessed and approached with caution. 

Terrain and Travel

  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Watch your sluff: it may run faster and further than you expect.
  • Watch for changing conditions today, storm slabs may become increasingly reactive.

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.