North Columbia

A spring-like mindset should be adopted as hazard will increase with daytime warming and solar radiation. 

Caution should be taken in sheltered and shaded areas where dry powder may be preserved and the persistent slab problem remains a concern.

The ridge of high pressure will start to break down with increasing cloud cover and the potential for light precipitation on Sunday afternoon.

Saturday Overnight: Mainly clear, some valley cloud may develop. Freezing level dropping to near valley bottom. Light southwest winds at ridgetop.

Sunday: Increasing cloud cover. Freezing level rising to around 1500 m in the afternoon. Light southwest winds at ridgetop.

Monday: Cloudy with snowfall. Freezing level around 1500 m. Strong northwest winds at ridgetop.

Tuesday: Mainly cloudy with light snowfall. Freezing level 500 to 1000 m. Light to moderate southwest winds at ridgetop. 

Earlier in the week, daily reports came in of human-triggered persistent slab avalanches on the January 30th surface hoar, 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. On Friday, large avalanches were triggered on this layer with explosives on solar aspects in the alpine and treeline. 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.

As the sun came out and temperatures rose in the afternoons, numerous wet loose avalanches have been observed on steep solar aspects in the past few days.

Several natural cornice failures have been observed in the past few days, a few of these cornice failures pulled pockets of wind slab on the slopes below.

Overnight, warmer temperatures and cloud cover may promote a weaker refreeze on the surface of the snowpack, particularly in the north of the region. A thin breakable crust exists on almost all aspects and elevations, while a thicker more prominent crust can be expected at lower elevations and on south-facing aspects. Warm daytime temperatures and the potential for some solar radiation, mainly in the south of the region, may cause these crusts to break down throughout the day.

Strong westerly winds throughout the week have created extensive wind-effect in open areas in the alpine and treeline. Expect to find old wind slabs on a variety of aspects, that will likely be unreactive to human triggering after several days of warm temperatures.

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

The facet/crust layer that formed in early December is 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.
• As surface loses cohesion due to melting, loose wet avalanches become common in steeper terrain.