High freezing levels, warm temperatures, strong UV inputs and poor overnight recovery have created moist snow below 2300m. This increases the likelihood of natural and human triggered avalanches, particularly in the afternoon.
Weather Forecast
Now until Friday, freezing level will hover around 1800m, temperatures will be seasonal -3 to -6C. Expect freeze thaw conditions. Mixed clouds and trace of snow rest of the week.
Snowpack Summary
Tuesday's warm temperatures softened alpine surface snow and weakened lower elevations snowpack making for moist/wet conditions. Slabs will persist at tree-line and above on North-Easterly aspects below ridge crests and cross-loaded terrain. The mid-pack is facetted, new snow interface is a concern along with a decomposed surface hoar down 40cm.
Avalanche Summary
Warm temperatures induced a natural avalanche cycle on Tuesday late afternoon. Size 3's noted in the alpine and size 2's at lower elevations. Highway 93 was subsequently closed in the late afternoon. Control work on Wednesday produced loose wet avalanches to size 2 that crossed the highway and wet slabs that showed propagation up to 100m across.
Problems
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.
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.