Avalanche Forecast

Archived

Jan 4th, 2021–Jan 5th, 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 avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

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, human triggered possible.

Regions

South Rockies.

Be cautious of slopes being loaded my new snow and wind where human triggered avalanches are likely.

Confidence

Moderate - Uncertainty is due to the track & intensity of the incoming weather system. Uncertainty is due to limitations in the field data.

Weather Forecast

Frontal systems cross the region on Monday night and again on Wednesday afternoon.

MONDAY NIGHT: 5-10 cm of snow, moderate southwest wind, treeline temperatures around -4 C.

TUESDAY: Flurries easing off in the morning then some sunny breaks in the afternoon, moderate to strong west wind, treeline temperatures around -6 C.

WEDNESDAY: Scattered flurries throughout the day with up to 5 cm of snow, moderate southwest wind, temperatures around -4 C.

THURSDAY: Scattered flurries 5-10 cm of snow, light northwest wind, temperatures around-6 C.

Avalanche Summary

Over the weekend there were numerous large (size 2-3) natural storm slab avalanches at alpine and treeline elevations, and some smaller (size 1) human triggered storm slabs. Natural and human triggered slab avalanches remain a concern with more snow and wind on the way on Tuesday. Triggering large persistent slab avalanches remains possible, even though few avalanches have been reported over the past month.

Snowpack Summary

New snow and wind will form fresh slabs on Monday night. Up to 10 cm of new snow will add to the 10-30 cm from the weekend, creating the potential for reactive slabs on steep wind-loaded slopes. The upper snowpack consists of several layers of old wind slabs, while the lower snowpack consists of decomposing crusts and weak faceted snow. Some large avalanches were reported on these deeper layers on Dec 23 and 25, but for the most part they have not been reactive over the past few weeks. However, this snowpack structure is always a concern on steep rocky slopes with variable snowpack depths.

Terrain and Travel

Avoid freshly wind loaded terrain features.
Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
Be aware of the potential for large avalanches due to the presence of buried weak layers.
Dial back your terrain choices if you are seeing more than 20 cm of new snow.

Problems

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.

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.