Watch for signs of changing stability as the temperature rises during the day.
Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
A warm, wet storm system will reach the coast early Monday. The interior should remain mostly dry for Monday but light flurries are possible in the afternoon. Temperatures will rise rapidly on Monday with the freezing level reaching around 1500m and winds increasing to moderate in the alpine. On Tuesday, the S. Columbia region will begin to see precipitation (5-10mm) and the freezing level are expected to rise to 2000m or higher. Wednesday is expected to be similar with freezing levels around 2000m and precipitation. Amounts are uncertain for Tuesday night and Wednesday with models currently showing 10-30mm. Strong alpine winds from the SW are expected for both Tuesday and Wednesday.
Avalanche Summary
There have been reports of isolated size 1 storm slab avalanches trigger by ski cuts. These are on NW-NE slopes in the alpine and I expect wind loading contributed. Also reports of loose sluffing from steep terrain features.
Snowpack Summary
15-20cm of new snow sits on a weak layer of surface hoar and/or a sun crust. In windier places, this new snow may have formed wind slabs in leeward features. Below around 1800m elevation and down around 20-30cm is a rain crust but it appears that the snow above it is generally well bonded. About 1m down, a weak layer of surface hoar and/or facets can be found in some locations. Snowpack tests on this layer are showing improving results, but in some locations "pops and drops" indicate this beast could still be touchy. A thick rain crust with facets from early November is buried over 1 m down. We may see these deep weak layers become a problem again with the upcoming storm system.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.