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Avalanche Forecast

Archived

Dec 12th, 2021–Dec 13th, 2021

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

Regions

South Columbia.

Wind slabs will be the main concern on Monday. Be on the lookout for stiff, drifted snow and signs of instability like shooting cracks as you enter wind-affected terrain.

Confidence

Moderate - Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack.

Weather Forecast

Sunday night: A trace of snow. Moderate southerly wind. Treeline temperatures around -8 C. Freezing level valley bottom.

Monday: Mostly cloudy with flurries up to 5 cm. Moderate southeast wind. Treeline temperatures around - C. Freezing level 600 m.

Tuesday: 5-10 cm of new snow. Light southwest wind. Treeline temperatures around -8 C. Freezing level valley bottom.

Wednesday: Mostly cloudy. Light southeast wind. Treeline temperatures around -10 C. Freezing level valley bottom.

Avalanche Summary

Wind slabs up to size 2 were reactive to ski cuts and explosives on Sunday. A limited natural avalanche cycle up to size 2.5 was reported to have run during the storm on Saturday. Noteworthy naturals include a size 3 on a northwest aspect in the Selkirks and a size 2 on an east aspect in the Monashees.

Reports from Wednesday and Thursday indicate an increase in persistent slab reactivity prior to burial by the current storm. There were several reports of natural size 2 avalanches in alpine terrain as well as several human triggered size 1 wind slabs around treeline. The most reactive slabs were on convex wind-affected slopes. Most avalanches were in the top 20-30 cm of snow.

Snowpack Summary

15-30 cm of recent snow has seen redistribution by strong wind at upper elevations. 

The defining feature of the snowpack is a prominent and widespread crust that reaches as high as 2400 m in the alpine now sits 40-70 cm below the surface. In many places, overlying snow is well-bonded to the crust but in others, weak faceted grains have been observed growing above it around treeline. Snowpack models show the faceting process progressing quickly at this elevation, likely due to the amount of heat and moisture trapped by the crust. We will be closely monitoring this layer going forward. The snowpack structure is relatively simple beneath the crust, with treeline snow depths around 100-200 cm.

Terrain and Travel

  • Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
  • Approach lee and cross-loaded slopes with caution.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.

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.