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Avalanche Forecast

Archived

Jan 5th, 2020–Jan 6th, 2020

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 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

North Columbia.

Continuing snowfall and wind are out-pacing the snowpack's ability to adjust. Stay vigilant with simple terrain choices as this pattern continues.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Sunday night: Cloudy, 10-20 cm of snow, moderate west wind with strong gusts, alpine temperature -11 C, freezing level dropping from 1000 m to valley bottom.

Monday: Mostly cloudy, isolated flurries with trace accumulations, light to moderate southwest wind, alpine high temperature -6 C.

Tuesday: Cloudy, 15-25 cm of snow overnight and throughout the day, moderate south wind, alpine high temperature -6 C.

Wednesday: Cloudy, 20-30 cm of snow overnight throughout the day, moderate west wind, alpine high temperature -6 C.

Avalanche Summary

Several human-triggered wind slabs were reported at treeline and alpine elevations on leeward features on Saturday. These avalanches broke 10-40 cm deep and were small in size (size 1-1.5). Additional snowfall and wind transport overnight may increase the size of these slabs on Monday.

Observers also reported large (size 2-3) avalanches breaking on a layer of surface hoar from late December on a variety of aspects and elevations from natural, human, and explosive triggers on Saturday and into Sunday. A few of these avalanches were triggered remotely (i.e. from a distance). 

Snowpack Summary

The most recent snow has been redistributed by strong southwest winds in exposed areas, loading lee features with stiffer, more reactive slabs. 

Over the past week, a total of 60-100 cm of snow has fallen burying a weak layer of feathery surface hoar and a hard melt-freeze crust on sun-exposed aspects. This layer has demonstrated reactivity past its due date as a storm slab interface, and it continues to produce large avalanches across aspects and elevations.

There are a couple more deeply buried weak layers, including a surface hoar layer from mid-December and a facet/crust layer from late November. Despite the significant load from recent snowfall and wind as well as a widespread, large natural avalanche cycle, avalanches have not been observed stepping down to these layers. 

Terrain and Travel

  • Avoid freshly wind loaded terrain features.
  • Be alert to conditions that change with elevation and wind exposure.
  • Be aware of the potential for large avalanches due to the presence of buried weak layers.
  • Remote triggering is a concern, watch out for adjacent and overhead slopes.

Problems

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.

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.