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Avalanche Forecast

Archived

Dec 25th, 2018–Dec 26th, 2018

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 best managed with patience and conservative terrain choices. Read more in the new forecaster blog here.

Confidence

Moderate -

Weather Forecast

The BC weather will take a holiday break over the next couple of days as the wild storm cycle of recent weeks eases in the Pacific.CHRISTMAS NIGHT: Freezing level at valley bottom, light southerly wind, no significant precipitation expected. BOXING DAY: Broken cloud cover, freezing level at valley bottom, light southerly wind, trace of snow possible. THURSDAY: Scattered cloud cover, freezing level at valley bottom, light northerly wind, no significant precipitation expected. FRIDAY: Scattered cloud cover, freezing level at valley bottom, moderate to strong south/southwest wind, 2 to 10 cm of snow possible.

Avalanche Summary

A natural size 3 avalanche was reported from a steep south facing aspect at 1500 m.  The avalanche likely failed on the ground running on what looked to be a grass slope from far away.A few large (size 2-3) natural persistent slab avalanches were reported on Sunday. These avalanches were reported on south aspects in the alpine and failed on failed on weak layers 150 cm below the surface. Natural activity has tapered off after an active period last week, when numerous persistent slab avalanches (up to size 3) were reported on all aspects (a few that even destroyed mature trees). The persistent slabs were 50-150 cm thick and likely failed on the early December weak layer. The same layer was responsible for several large human triggered avalanches earlier this month (see this MIN report for an example), and although there are no recent reports of human triggered avalanches, professionals are still being very cautious with their terrain choices because of this layer.

Snowpack Summary

Low density snow from the past few days sits above wind affected snow in the alpine and around treeline.A weak layer that formed during the dry spell in early December is now 80-120 cm deep. The layer is composed of weak facets, surface hoar, and a sun crust on steep south-facing slopes. This layer has been responsible for large persistent slab avalanches over the past two weeks, particularly on northeast facing slopes between 1900-2300 m and on steep south-facing slopes in the alpine.Another weak layer from mid-November is now buried up to 150 cm and a crust that formed in late October is found near the bottom of the snowpack. The probability of triggering these deeper layers is low, but the most suspect areas would be shallow spots in steep rocky terrain.

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.