North Columbia

Heavy snowfall and strong winds Saturday night are expected to create dangerous avalanche conditions for Sunday. It is recommended to avoid avalanche terrain in heavy snowfall areas.

On Friday, we received reports of many natural, explosive, and human-triggered storm slab and wind slab avalanches from all aspects. The majority of this activity occurred at treeline and in the alpine, and was typically around size 2 with a few up to size 3. The typical release depth of these avalanches varied from 20 to 60 cm.

Clear skies from the past few days allowed for observations of many deep persistent slab avalanches as well as explosive control missions, which produced large to very large (size 2 to 3.5) avalanches. They were on all aspects and between 2200 m and 2800 m in elevation. Although many of the avalanches occurred in unrideable terrain, they are evidence that the layer is still triggerable. Riders should continue to avoid thin snowpack areas, which are often found near ridgelines.

The storm is expected to be most intense Saturday overnight bringing substantial amounts of new snow for Sunday. This new snow will bury the interface from the recent period of cold Arctic air which includes reports of surface faceting, small surface hoar in sheltered areas, and widespread wind-affected surfaces and wind slabs in exposed terrain at higher elevations resulting from the recent northeast outflow winds. Below this interface is 20-50 cm of older storm snow from the beginning of last week.

Around 80 to 100 cm of snow may rest on a small layer of surface hoar crystals that was buried mid-February. This layer is most likely found around treeline elevations in areas sheltered from the wind. This layer generally appears to be dormant now but could still be capable of producing avalanches in isolated areas. The remainder of the mid-pack is generally strong.

A layer of large and weak facets that formed in November is deeply buried, found near the base of the snowpack. The likelihood of human triggering this layer is currently low given its depth. However, it is still best to avoid steep, thin, rocky slopes near ridges at alpine and upper treeline elevations.

Saturday Night

Snowfall 20-40 cm, moderate to strong SW wind, treeline low around -18 °C.

Sunday

Snowfall 5-15 cm, moderate SW wind, treeline high around -10 °C.

Monday

Light snowfall up to 5 cm overnight, tapering off in the morning, light SW wind, treeline high around -10 °C.

Tuesday

Mainly cloudy with a chance of light flurries, light SE wind, treeline high around -8 °C.

More details can be found in the Mountain Weather Forecast.

• Avoid all avalanche terrain during periods of heavy snowfall.
• Use increased caution at all elevations. Storm snow is forming touchy slabs.
• Approach steep open slopes at and below treeline cautiously, buried surface hoar may exist.
• Storm slabs in motion may step down to deeper layers resulting in large avalanches.
• Avoid shallow, rocky areas where the snowpack transitions from thick to thin.