Avalanche Forecast

Issued: Jan 31st, 2017 4:49PM

The alpine rating is considerable, the treeline rating is moderate, and the below treeline rating is low. Known problems include Storm Slabs and Persistent Slabs.

rbuhler, Avalanche Canada

Cariboos.

The recent storm snow is expected to remain reactive to triggering on Wednesday. In the south, the main problem is isolated wind slabs. In the north, a more widespread storm slab problem may exist.

Summary

Confidence

Moderate -

Weather Forecast

A ridge of high pressure keeps the region cold and dry for the next few days. Wednesday and Thursday are expected to sunny with light northeast wind and treeline temperatures around -15C. Increasing cloud cover is expected on Friday in advance of a weak storm system which is currently forecast to arrive early Saturday.

Avalanche Summary

On Monday, several natural wind slab and storm slab avalanches up to size 2.5 were reported. These slabs were typically 30-50 cm thick and failed on a variety of aspects at treeline and in the alpine. Skiers also triggered several size 1 slabs. On Sunday, a skier triggered a size 1 wind slab north of Wells Grey on a northeast aspect which was 5-15 cm thick.On Wednesday, recently formed storm slabs and wind slabs are expected to remain reactive to human triggering, especially on steep and unsupported or convex slopes. Winds have recently switched from south to north and wind slabs should be expected on all aspects.Persistent slab avalanches also remain a serious concern for the region. Last week there were numerous large human triggered avalanches and several of these avalanches involved multiple people being buried. These avalanches all released on or stepped down to the mid-December weak layer down 1-1.5 m in the snowpack. Check out this list of recent near misses which includes many in the Cariboo region.

Snowpack Summary

10-60 cm of new snow accumulated on Sunday and Monday with the largest amounts in the north of the region. Strong shifting winds have formed wind slabs on a variety of aspects in wind exposed terrain. The mid-January interface is now down 50-100 cm and consists of buried surface hoar in sheltered areas, old wind slabs in exposed terrain, and/or widespread faceted old snow. The interface has generally stabilized but isolated weaknesses may still exist where buried surface hoar is preserved. The mid-December surface hoar/facet weakness is now found down 70 cm in shallow snowpack areas, or as much as 1.5 m in deeper snowpack areas. This layer woke up during the last storm and has remained reactive to human triggers. This weak layer is responsible for several large human-triggered avalanches, including some with multiple burials, and the layer may continue to remain reactive for the foreseeable future. Click here for a new blog post with more details.

Problems

Storm Slabs

In places the received more than around 30 cm of new snow, storm slabs are expected to be reactive to triggering. In the south of the region, wind slabs are expected to be the primary concern.

Avoid areas where the surface snow feels stiff or slabby.Use caution in lee areas in the alpine and treeline. Storm snow will form slabs.The new snow will require several days to settle and stabilize.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 2

Persistent Slabs

The persistent weakness buried mid-December has been responsible for several large human-triggered slab avalanches and subsequent burials last week. These deeper weaknesses can still be triggered with nasty consequences.

Be aware of the potential for large, deep avalanches due to the presence of buried weak layers.Use conservative route selection, choose moderate angled and supported terrain with low consequence.Avoid shallow snowpack areas where triggering is more likely.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2 - 4

Valid until: Feb 1st, 2017 2:00PM