South Columbia

The snowpack is complex and quite variable right now. Buried weak layers remain reactive and conservative terrain selection remains critical. Extra caution is required during the heat of the day, especially on sun exposed slopes and around cornices.

Moderate - Timing or intensity of solar radiation is uncertain

A mix of sun and cloud is expected for Friday with moderate southwest winds in the alpine. A temperature inversion is expected with a layer of above-freezing air sitting around 2000m elevation and colder temperatures in the valleys. A weak storm pulse is expected to bring 5-10cm to the region on Saturday morning. Alpine winds are expected to be moderate from the southwest on Saturday with freezing levels around 1800m. Mostly dry conditions are expected Saturday afternoon through Sunday morning before a second weak storm pulse arrives Sunday afternoon.

On Wednesday, skiers triggered two size 2 persistent slab avalanches. The first was on a northeast aspect at 1900m and released on the layer of surface hoar down 30-40cm that was buried last weekend (Feb 21). The second was on a northeast aspect at 1850m and released on the surface hoar down 45cm that was buried at the beginning of February. Natural sluffing up to size 2 was also reported from steep south and west aspects in the alpine. On Tuesday, numerous natural and skier triggered avalanches up to size 2 were reported. This included isolated wind slabs, loose dry sluffing from steep sunny slopes, and large cornice releases. There is a lot of uncertainty for how reactive the snowpack will continue be on Friday with the continued warm temperatures and sun. I expect that the buried weak layer from early February will continue to produce large destructive avalanches with heavy triggers such as cornice falls or smaller avalanches stepping down, but it may also still be possible to directly trigger this layer in some areas. Sluffing can be expected from steep sun exposed slopes and cornices will become weak with daytime warming and sun.

Surface hoar growth is being reported on all aspects and elevations up to 10mm and a sun crust has formed on south facing slopes. A weak layer of surface hoar and/or a sun crust buried February 21 can be found 15-60cm below the surface. This layer is reported to be increasing in reactivity in the deeper snowfall areas as the recent low density storm snow continues to settle into a cohesive slab. The surface hoar and/or crust layer which was buried February 10 is now down 60-100cm and has been responsible for some very large avalanches recently. This layer is expected to become most reactive during the heat of the day, especially on sun exposed slopes. Large cornices remain a concern and will become weak with daytime warming.