North Columbia

New storm snow will add to the complexity of an already tricky snowpack. Looks like a good day to make conservative terrain choices.

Moderate - Intensity of incoming weather systems is uncertain on Tuesday

Tuesday Night: 10-15cm of new snow / Strong southwest winds / Alpine temperature of -9Wednesday: Generally overcast skies / Moderate northwest winds / Alpine temperature of -13Thursday: Mix of sun and cloud with scattered flurries / Light and variable winds / Alpine temperature of -17Friday: Overcast skies / Moderate northwest winds / Alpine temperature of -10

In Rogers Pass on Monday, skiers remotely triggered a size 3.5 persistent slab avalanche from 40 m away on a south-facing, cross-loaded slope at 2600 m. Although deeper, persistent avalanche activity is becoming less frequent, this avalanche points to the continued reactivity and destructive potential of these layers. On the same day, explosives control in the Monashees triggered more persistent slab avalanche activity to size 3 in north to east facing alpine terrain. Recently formed wind slabs to size 2 were also ski cut in wind-exposed, higher elevation terrain.Looking forward, expect a new round of storm slab activity in response to new snow and wind on Tuesday night. Extensive storm loading has the potential to re-activate deeper, more destructive persistent weak layers.

By Wednesday morning I would expect up to 30cm of new snow. Forecast strong ridgetop winds are expected to redistribute the new snow into much deeper, reactive slabs in wind-exposed terrain. The new snow will overlie older wind slabs and a rain crust below 1600m.Below the snow surface, several persistent weak layers make up a troublesome snowpack. In the top 1.5-2.5 m of the snowpack, two surface hoar layers buried in January can be found. Expect to find one or other of these on all aspects and elevations.Deeper in the snowpack (around 200 cm deep) is a facet/crust/surface hoar layer from December, most prevalent at and below treeline.Near the base of the snowpack is a crust/facet combo, most likely to be triggered from thin spots in the alpine.All of these layers have produced large avalanches recently. The wide distribution and ongoing reactivity of these layers suggests that avoidance through choosing simple terrain is the best strategy.