North Columbia

A week of heavy snowfall has left the snowpack primed for large human triggered avalanches.

Moderate - Forecast snowfall amounts are uncertain.

THURSDAY NIGHT: Lingering flurries overnight with 5-15 cm of snow, strong wind from the southwest, freezing level rapidly dropping, alpine temperatures drop to -12°c. FRIDAY: Isolated flurries in the morning then clearing in the afternoon, moderate wind from the west, alpine temperatures around -10°c. SATURDAY: Clear in the morning then increasing cloud throughout the  day, light wind from the south, alpine high temperatures around -8°c. SUNDAY: Cloudy with scattered flurries and 2-5 cm of snow, light wind from the southwest, alpine high temperatures around -6°c.

Thursday's storm likely resulted in another active avalanche cycle. Over the past week there has been regular storm slab and persistent slab avalanche activity, producing many large avalanches (size 2-3). Natural activity has occurred during the steady pulse of storms. Skiers have also been able to trigger smaller (size 1-1.5) storm slabs and wind slabs on small freshly loaded terrain features, as well as remotely trigger some large (size 2-2.5) persistent slab avalanches on adjacent slopes. The most recent remotely triggered avalanche failed on a layer of surface hoar down 80 cm on Tuesday. Remote triggering indicates a touchy weak layer that could take awhile to gain strength.

Recent storms have deposited 80-120 cm of new snow. This new snow sits on a weak layer of facets (sugary snow), surface hoar (feathery crystals), and a sun crust (on south aspects). Strong winds have promoted widespread slab formation, particularly with the most recent new snow available for transport. A weak layer from mid November is now buried up to 150 cm and consists of surface hoar and a sun crust. The potential may exist for smaller avalanches to step down and trigger this deeper layer, resulting in large avalanches. The most likely place for this layer to be a problem is on steep, south facing slopes at treeline where the surface hoar sits on the sun crust. At the base of the snowpack is a crust that formed in late October. Concern for this layer is dwindling but it may still be worth considering in places such as steep, rocky, alpine terrain, especially where the snowpack is shallow.