South Columbia

Cool conditions are expected to improve stability this week but tricky conditions may persist on Wednesday, especially at higher elevations. Storm and persistent slabs may still be reactive to human-triggering and very large avalanches are possible.

Fair - Freezing levels are uncertain

A ridge of high pressure builds on Wednesday and should result in mainly dry conditions for the next few days. On Wednesday, a mix of sun and cloud is expected with moderate-strong alpine winds from the NW that should ease through the day. Isolated flurries are possible. Freezing levels are expected to fall to around 1000m Tuesday overnight and then reach around 1500m on Wednesday afternoon. On Thursday and Friday, similar conditions are expected with mainly dry conditions, a mix of sun and cloud, and light alpine winds. Freezing levels are expected to reach 1600m on Thursday afternoon, 1800m on Friday afternoon, and below 1000m during each overnight period.

On Monday, a few slab avalanches were reported above around 2200m elevation as well as lots of wet sluffing at lower elevations. Several slabs up to size 2.5 were triggered by cornice failures. Some of these were up to 1m deep and these are expected to be failing on persistent weak layers. On Saturday and Sunday, isolated natural size 2-3 persistent slabs were reported on a variety of aspects and mainly above 2000m. On Thursday and Friday, a widespread avalanche cycle occurred in response to wet and windy conditions. These were a mix of storm slab, loose wet avalanches and persistent slabs up to size 3. Natural avalanches are generally not expected on Wednesday if there is good overnight recovery but may still be possible in isolated areas. Human-triggered storm slabs and persistent slabs are still a concern, especially on steep, unsupported slopes in the alpine. Stability is generally expected to improve with the cooling trend but this may take a few days and touchy conditions may still exist on Wednesday.

20-40cm of heavy storm snow overlies a thick rain crust that formed last Friday when it rained into the alpine. A new surface crust is expected to be widespread on Wednesday after freezing levels drop Tuesday overnight. On Monday, moist snow was being reported to around 2600m in the south of the region and 2100m in the north so the crust will likely extend well into the alpine. In the high alpine, strong winds have redistributed the new snow and wind slabs can be expected in leeward terrain features. Several persistent weak layers exist in the upper 1m of the snowpack and remain a concern. The mid-March crust/facet layer is down around 60cm and remains reactive to light triggers. Down around 80cm is the mid-February crust/facet/surface hoar layer which has also been reactive to heavy loads like avalanches in motion stepping down, cornice failures, or explosives. Both layers have the potential for wide propagations and very large avalanches are possible.