North Columbia

The North Columbias have been a hotspot for persistent slab activity and a dump of new snow is just going to make it worse. Expect stability to deteriorate over the day.

High -

Thursday night: Cloudy with continuing flurries bringing around 10 cm of new snow. Light southwest winds increasing to strong in the alpine.Friday: Cloudy with continuing flurries bringing 10-15 cm of new snow and new snow totals to 20-25 cm. Snowfall continuing overnight. Moderate to strong southwest winds. Alpine high temperatures around -5.Saturday: Cloudy with easing flurries bringing up to 5 cm of new snow and new snow totals to 35-45 cm. Light snowfall continuing overnight. Moderate southwest winds easing over the day. Alpine high temperatures around -7 and dropping over the day.Sunday: Cloudy with isolated flurries and a trace to 5 cm of new snow and new snow totals to 40-50 cm. Light northeast winds. Alpine high temperatures around -20 and continuing to fall over the day.

The mid-January Surface hoar seems to be most sensitive in this region. Two more small (size 1-1.5) persistent slabs were triggered by skiers in the Monashees on Wednesday. They occurred on north and south aspects at 1700 m.On Tuesday there was quite a bit of activity from solar aspects throughout the region. In the neighboring Glacier National Park, a size 3 avalanche was skier triggered on a steep southeast facing slope in the alpine. More details and photos here. Skier triggered avalanches from size 1.5 to 2.5 were reported from south and southeast facing terrain between 2300 and 2500 m. Clear skies allowed for increasingly strong late January sun, which was likely a factor in these avalanches. Another size 2.5 persistent slab failed naturally on a northeast facing feature at 1900 m. Two more reports came in Monday of skiers triggering persistent slab avalanches to size 1.5 on a variety of aspects between 1500 and 1800 m. This MIN post and this one (from the neighboring South Columbias) do a great job of illustrating the nature of this problem which is most prevalent between 1400 and 1900 m. This interface will likely wake up as storm snow begins to stack up over the weekend.

New snow has begun to accumulate on the previous surface, which consists of a mix of sastrugi, stubborn old wind slabs, facets, crust and surface hoar. The new snow is unlikely to bond well to these surfaces over the near term. Last weekend's warm and windy weather left a crust up to 3 cm thick on steep south and some west facing aspects and redistributed quite a bit of snow into wind slabs in lee features at treeline and above. These older wind slabs are now probably only suspect in extreme terrain. The warmth also allowed 25 to 50 cm of older snow to continue to consolidate above the mid-January persistent weak layer (PWL). This PWL is made up of large surface hoar that is most prevalent at treeline and below, with enhanced reactivity noted between 1400 and 1900 m. On steep solar aspects this interface presents as a crust, there may be locations where surface hoar actually sits on the crust. Potential exists for this layer to become increasingly reactive as new snow adds load to the snowpack. Slab releases or loose snow avalanches formed of new snow may also act as a trigger for this layer.The middle and lower portions of the snowpack are generally well-settled and strong.