North Columbia

A Special Public Avalanche Warning is in effect. Copy this link to view details: http://bit.ly/2nSOUyX

Moderate - Intensity of incoming weather systems is uncertain on Tuesday

MONDAY: Mainly sunny, with increasing clouds late in the day. Light winds. Treeline temperature near -10.TUESDAY: 10-15 cm snow. Moderate westerly winds. Treeline temperature near -5.WEDNESDAY: Flurries. Light winds. Treeline temperature near -8.More details can be found in the Mountain Weather Forecast.

A very large, widespread avalanche cycle was observed on Thursday, with a few events continuing on Friday. Slopes of all aspects and elevations ran full path and reached valley floor. In some cases, mature timber was smashed. These failed on all of the persistent weak layers discussed in the snowpack section. Avalanches involving only the recent storm snow were also very large. Explosives continued to produce very large persistent slabs on Saturday.The natural cycle has wound down, but human-triggering remains a real concern. Avalanches are most likely to be triggered with a large load (like a snowmobile landing a jump, a cornice fall, or a solar-triggered avalanche stepping down), or from a thin-spot trigger point, like around trees or rocks. You might be surprised by how large an avalanche can be triggered and how far it could run.

Strong north to north-westerly winds have shifted 25-70 cm recent storm snow into wind slabs on lee slopes. This adds to an existing storm slab that's 1-2.5 m deep from the last couple of weeks' accumulation. Several persistent weak layers make up a troublesome snowpack. In the top 1.5-2.5 m of the snowpack, two surface hoar layers buried in January can be found. Expect to find one or other of these on all aspects and elevations.Deeper in the snowpack (around 200 cm deep) is a facet/crust/surface hoar layer from December, most prevalent at and below treeline.Near the base of the snowpack is a crust/facet combo, most likely to be triggered from thin spots in the alpine.All of these layers have produced large avalanches recently. The wide distribution and ongoing reactivity of these layers suggests that avoidance through choosing simple terrain is the best strategy.