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Avalanche Forecast

Archived

Dec 21st, 2023–Dec 22nd, 2023

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

Regions

Glacier.

A persistent weak layer of surface hoar mid-snowpack, is primed for human triggering. The safest way to manage this problem is through conservative terrain use.

Pushing into bold terrain in search of untracked lines, has resulted in several near-misses recently.

Confidence

Moderate

Avalanche Summary

On Wed/Thurs, several natural avalanches up to size 2.5 were observed running from the steep terrain of Mt. Macdonald.

Five significant human-triggered avalanches have occurred in the past week, all failing on the Dec 1st surface hoar layer. In the Connaught drainage a size 2.5 was triggered on Balu Peak, on Ursus Minor a skier narrowly avoided being carried over some cliffs, and in the Asulkan valley another avalanche was triggered near the 7 steps.

Snowpack Summary

Thurs's warm temps made for moist snow up to 2000m and up to 25cm overlies variable old surfaces: wind affect; a crust on steep, solar slopes; or surface hoar in sheltered areas.

The Dec 1 surface hoar, down 50-100cm, continues to produce 'sudden' results in tests and has been the culprit in several recent close calls from skier-triggered avalanches. Below 2100m, a rain crust is buried 40-50cm deep.

In shallow areas the base of the snowpack is faceted and unsupportive.

Weather Summary

A decent storm will bring new snow, high winds and as it leaves, cold temps.

Tonight: Trace precip, Light SW wind, Freezing level (Fzl) 1500m

Friday: 17cm, High -3°C, Mod-Strong SW wind, Fz lvl 1700m,

Saturday: Mix of sun/cloud. Low -14°C, High -11°C Mod SW Winds. Fz lvl valley bottom

Sunday: Mixed sun/cloud, Low -13°C, High -7°C, Light W wind. Fz lvl 900m

Terrain and Travel Advice

  • Be mindful that deep instabilities are still present and have produced recent large avalanches.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.

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.