South Columbia

The recent storm snow is expected to be touchy on Sunday, especially in wind loaded terrain and on sun exposed slopes. Conservative terrain selection remains critical.

Moderate - Timing or intensity of solar radiation is uncertain

A ridge of high pressure is expected to keep the region dry for the next few days. Mostly sunny conditions are expected on Sunday with a few clouds and moderate alpine wind from the northwest. Freezing levels are forecast to reach around 1000 m or so in the afternoon. Sunny conditions are expected for Monday and Tuesday with mainly light alpine wind on Monday and moderate wind on Tuesday. Freezing levels are forecast to climb to around 2500 m on Monday and remain there on Tuesday. A temperature inversion will likely develop and temperatures may be colder at valley bottom than in the alpine.

On Thursday and Friday, widespread natural and human-triggered storm slab avalanches up to Size 3 were reported throughout the region. It appears that the natural activity likely peaked Thursday overnight. Most of the reported avalanches on Friday had slab thickness of 30-60 cm but a few were reported to be up to 1 m thick. A few remotely triggered avalanches have also been reported recently from up to 20 m away. On Sunday, the recent storm snow is expected to remain reactive to human triggering, especially in wind affected terrain. A lingering weak layer below the recent storm snow may increase the size and propagation potential of avalanches. Extra caution is recommended during the heat of the afternoon, especially on sun exposed slopes. This will become increasingly important on Monday and Tuesday as freezing levels climb. We are entering the first period of substantial warming following months of sustained cold conditions. Any weaknesses lingering in the snowpack will be tested in the coming days.

40-70 cm of storm snow has accumulated of the past few days. Recent strong winds from the south and west have redistributed this snow in exposed terrain forming touchy wind slabs. Weaknesses exist within this recent storm snow with reports of 'upside-down' conditions and easy shears within the top 70 cm. All this new snow is also bonding poorly to the previous snow surface from early February that includes sun crust on steep sun-exposed slopes, faceted snow, as well as surface hoar on sheltered open slopes. The mid and lower snowpack are generally well settled and stable in deeper snowpack areas but may be faceted and weaker in shallower areas.