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Avalanche Forecast

Archived

Dec 22nd, 2023–Dec 23rd, 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 unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Glacier.

Fresh snow and wind will create a new reactive storm slab, watch for signs of instability.

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.

Confidence

Moderate

Avalanche Summary

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

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

High freezing levels have left moist snow up to ~2000m, this will form a crust as it cools. 15-25 cms of new snow has fallen over the last few days with wind creating wind slabs at ridgetop

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

After Friday's storm we'll see high-pressure building, giving cooler temps and some sun.

Tonight: Trace precip, wind: westerly 20-30km/hr, Freezing level (Fzl) at VB

Saturday: Mix of sun/cloud. Temp: High -10°C, Winds: 15 gusting 40km/hr. Fz lvl 600m

Sunday: Mixed sun/cloud, Temp: High -6°C, Light South wind. Fz lvl 1000m

Monday: Mixed sun/cloud, Temp: High -7°C, light South wind. Fz lvl 1000m

Terrain and Travel Advice

  • Be mindful that deep instabilities are still present and have produced recent large avalanches.
  • Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.

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.