A warm, wet, and windy storm is expected to result in natural avalanche activity by morning.
Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain on Sunday
Weather Forecast
Overnight and Sunday: Strong Southwest winds and heavy precipitation overnight and during the day Sunday. Freezing level rising to near 2000 metres and remaining there through Sunday.Monday: Winds becoming moderate Westerly and then light from the Northwest as the precipitation ends and the freezing level drops down to about 1000 metres. Chance of broken skies in the afternoon.Tuesday: Freezing down to valley bottoms overnight. Mostly sunny during the day with light Westerly winds and freezing levels climbing up to about 1500 metres.
Avalanche Summary
There was widespread avalanche activity reported from Friday. Natural storm snow avalanches up to size 3.5 from big features on South aspects, and remotely triggered storm slabs up to size 3.5. There were a couple of natural persistent slab avalanches up to size 3.0 that featured long fracture propagations connecting terrain features. Forecast warm temperatures, strong Southwest winds, and heavy precipitation are expected to result in widespread natural avalanche activity.
Snowpack Summary
Warm temperatures have resulted in the 50-80 cm of storm snow settling into a cohesive slab above the mix of crusts, facets, and surface hoar that was buried on March 2nd. The storm slab may be up to 150 cm deep where it has been transported by the wind. These deep deposits may feel "upside down", with more dense and maybe even moist snow above drier lighter snow. Forecast snow, warm temperatures, and wind is expected to add a new load to this developing storm slab. The early February persistent weak layer continues to show sudden planar or collapse characteristics buried down 80-180 cm in snow profile tests , and it is a concern for long fracture propagations and remote triggering. Moist or wet snow below treeline may not be well bonded to the old melt-freeze crust, and may release naturally with more warm temperatures and possibly rain.
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.