Avalanche Forecast

Archived

Dec 28th, 2019–Dec 29th, 2019

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

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.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

Cariboos.

The persistent slab problem is evolving into a low probability/high consequence scenario where you may not observe any indication of instability before making a dangerous decision. The formation of new wind slabs up high will add a layer of complexity to terrain selection.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

Saturday night: Mostly cloudy, isolated flurries with trace accumulation, alpine low -9 C, alpine wind moderate from the southwest.

Sunday: Scattered cloud, alpine high -7 C, alpine wind light southwest.

Monday: Scattered cloud, flurries starting in the pm accumulating 5-10 cm overnight. Alpine high -7 C, alpine wind building through the day to strong west overnight.

Tuesday: Mostly cloudy, flurries accumulating up to 5 cm, alpine high -5 C, alpine wind tapering to light west by evening.

Avalanche Summary

Small loose dry avalanches were observed out of extreme terrain over the weekend. No new slab avalanche activity has been reported since Monday.

Last weekend there were reports of numerous natural and explosive triggered avalanches up to size 2.5

Snowpack Summary

Moderate westerly winds are likely to have blown around 15-30 cm of new snow, forming soft windslab in alpine lees. Anywhere from 60 to 120 cm of snow is resting on a widespread layer of large, feathery, surface hoar which we're calling the "December 12th Surface Hoar." This layer was the culprit for the large natural avalanche cycle last week. Activity on this interface has likely tapered off, but there remains some uncertainty as to how quickly the snowpack is gaining strength.

A weak layer formed in late November is now buried around 1 m or more below the surface. This interface may present as surface hoar, a crust, facets or a combination, depending on elevation and aspect.

Terrain and Travel

Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
Caution around convexities or sharp changes in terrain.
Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
Avalanche hazard may have improved, but be mindful that deep instabilities are still present.

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.