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Avalanche Forecast

Archived

Nov 24th, 2021–Nov 25th, 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 and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
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.

Regions

South Columbia.

Incoming storm with heavy snow and wind will increase the avalanche hazard: expect a natural avalanche cycle Friday. Thursday will be more tricky as the storm snow accumulates and approaches a tipping point. Use increasing caution especially where the snow is wind affected.

Confidence

High - We are confident the likelihood of avalanche will increase with the arrival of the forecast weather. Uncertainty is due to the complexity of the snowpack’s structure.

Weather Forecast

Wednesday Overnight: Weather system arriving overnight with 10 to 15 cm of snow and moderate to strong south west wind.

Thursday: Stormy day with warming temperatures raising freezing level to around 1200m. 15 to 25 cm of additional new snow. Continued moderate to strong south or southwest wind

Friday: By the end of the day it looks like another 15 to 25 cm bringing storm totals around 40 to 65 cm. Winds will start to ease and veer to the west as the storm ends. Temps will start to cool from the peak warming (when the freezing level rose to around 1500m).

Saturday: A brief cooler, drier, calmer day before the next system arrives.

Avalanche Summary

Get ready for a direct action avalanche cycle driven by lots of new snow and honking wind! With 65 cm of new snow by Friday, and possibly even more, falling in the alpine combined with strong south to west winds I expect size 2 storm slabs will be common on any aspect with the best candidates being slopes above 1200m and steeper than 30 to 35 degrees. Windslabs on lee and crossloaded slopes will be even more likely and bigger, up to size 3 is possible.

Remember, if you see slopes that have avalanched, similar slopes (same aspect, elevation, steepness, terrain feature) are prime candidates for something similar.

Snowpack Summary

The snowpack summary is available here.

Terrain and Travel

  • Watch for rapidly changing conditions during periods of heavy loading from new snow, wind, or rain.
  • As the storm slab problem gets trickier, the easy solution is to choose more conservative terrain.
  • Expect slab conditions to change drastically as you move into wind exposed terrain.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.

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.