North Columbia

Danger remains elevated at treeline with an ongoing concern for persistent slab avalanches. Use extra caution in shaded and sheltered areas where triggering persistent slab avalanches is most likely.

Avalanches are unlikely in areas where a hard surface crust is present.

A passing frontal system will bring a more unsettled weather pattern with light snowfall expected throughout the week.

Sunday Overnight: Increasing cloud cover. Light southwest winds at ridgetop. Freezing level lowering to 500 m.

Monday: Cloudy with light snowfall. Light westerly winds at ridgetop. Freezing level around 1000 m.

Tuesday: Cloudy with light snowfall. Light to moderate northwest winds at riddgetop. Freezing level rising to 1000 m in the afternoon.

Wednesday: Cloudy with light snowfall. Light to moderate northwest winds at ridgetop. Freezing level rising to 1300m in the afternoon.

Earlier last week, near-daily reports came in of human-triggered persistent slab avalanches on the January 30th weak layer, with the associated surface hoar layer taking both recreationists and professionals by surprise. Reactivity has begun to taper but this buried weak layer should not be taken lightly as it may now present a low-probability, high-consequence problem. The most reactivity on this layer has been seen between 1600-2200 m in open areas in the trees, in cut blocks and on steep convexities.

On Saturday, a large natural persistent slab avalanche occurred on a south-facing aspect in the alpine, potentially as a result of warm temperatures and strong solar radiation. On Friday in the South Colombia, large persistent slab avalanches were triggered with explosives on solar aspects in the alpine and treeline. 

New snow is expected to bond poorly to the old surface. This surface is comprised of near-surface faceting and in some areas, surface hoar growth overlying a melt-freeze crust at lower elevations, a sun-crust on steep solar aspects, and hard wind-affected snow in the alpine and exposed treeline. 

Several weak layers exist in the upper snowpack including buried crusts, facets, and a prominent weak layer of buried surface hoar. This surface hoar has been the dominating feature in the past few weeks. It was buried in late January and exists 40 to 100 cm deep in the snowpack. The surface hoar is most prominent in sheltered openings at and below treeline.

The facet/crust layer that formed in early December is now buried around 120 to 250 cm. The last reported avalanche was on January 31 from a large explosive, and before that on January 23. Although unlikely, the layer could be triggered from a large load like a cornice fall or a shallower slab avalanche could step down to this layer. Humans are unlikely to trigger it, with perhaps the exception in thin, shallow snowpack areas. Check out the forecaster blog for more information.

• When a thick, melt-freeze surface crust is present, avalanche activity is unlikely.
• Be aware of the potential for large avalanches due to the presence of buried surface hoar.
• Surface hoar distribution is highly variable. Avoid generalizing your observations.