Avalanche Forecast

Archived

Dec 20th, 2023–Dec 21st, 2023

Alpine

Natural avalanches unlikely, human triggered possible.

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.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

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 Wednesday, there were a few size 1-2 windslab avalanches from the steep terrain above the Eastern portion of the highway corridor.

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

Up to 25cm of soft snow overlies variable old surfaces: wind affect; a thin sun crust on steep, solar slopes; or surface hoar in sheltered treeline areas.

The Dec 1 surface hoar, down 50-100cm, continues to produce 'sudden' results in snowpack tests and has been the culprit in several recent close calls from human-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 relatively benign weather pattern is in place over our area until the end of the day Friday.

Tonight: Isolated flurries, Alpine low -4°C, 1500m freezing level (fzl), Light SW ridgetop winds.

Thurs: Scattered flurries (5cm), High -2°C, 1700m fzl, Light SW wind.

Fri: Flurries (15cm), Low -8°C, High -3°C, 1400m fzl, Moderate SW wind.

Sat: Mixed sun/cloud, Low -13°C, High -9°C, Light W wind.

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.
Early season avalanches at any elevation have the potential to be particularly dangerous due to obstacles that are exposed or just below the surface.

Problems

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.

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.