Avalanche Forecast

Archived

Dec 20th, 2021–Dec 21st, 2021

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Below Threshold.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Below Threshold.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Below Threshold.

Regions

Yukon.

New snow and extreme wind are expected to induce a natural avalanche cycle and make mountain travel downright inhospitable. Avoid all avalanche terrain Tuesday.

Confidence

Low - Forecast precipitation (either snow or rain) amounts are uncertain. Uncertainty is due to the limited number of field observations.

Weather Forecast

Prepare for wind my friends.

MONDAY NIGHT: Overnight low temperature around -15, moderate to strong west/southwest wind, 5 to 10 cm of snow.

TUESDAY: Overcast, daytime high temperature around -12, strong to extreme north/northeast wind, 2 to 6 cm of snow possible.

WEDNESDAY: Broken cloud cover, daytime high temperature around -15, strong to extreme north/northwest wind, no snow expected.

THURSDAY: Broken cloud cover, daytime high temperature around -18, strong north wind, no snow expected.

Avalanche Summary

This MIN from Saturday shows a small wind slab in a terrain feature known for producing these kinds of avalanches. Other than that, we haven't had any recent avalanche observations, it was pretty quiet and beautiful in the White Pass last weekend.

On December 1, a size 2.5 avalanche was remotely triggered by a recreational group on Log Cabin. This avalanche likely failed on the weak, sugary snow at the bottom of the snowpack.

Snowpack Summary

There was a glorious inversion in place, and small surface hoar has formed where there was valley fog, like a ring around a bathtub. It all changes Monday night as wind picks back up, and it begins to snow once again. Widespread fresh storm slabs are expected to be forming Tuesday.

The middle snowpack is supportive to travel but snow depth still varies greatly with aspect and elevation.

A layer of weak, sugary snow at the base of the snowpack has been observed in most areas. This layer has been inactive since early December, but it might still be possible to trigger this deeply buried layer in shallow snowpack areas. A cornice fall or surface avalanche impacting a slope may also have the potential to trigger it.

Terrain and Travel

Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
Storm slabs in motion may step down to deeper layers resulting in large avalanches.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.