Confidence
Fair - Timing, track, or intensity of incoming weather is uncertain
Weather Forecast
Monday: A cold front brings moderate to heavy snow overnight Sunday. This is forecast to continue on Monday until the front departs in the afternoon. Moderate to strong south-westerly winds, switching to north-westerly and decreasing. Freezing level around 1200m, falling to around 900m.Tuesday: A brief ridge of high pressure should bring a break in precipitation and possibly clear skies and sunshine, although northern areas may cloud over by afternoon. Light winds. Cool temperatures, except in areas with direct solar warming.Wednesday: North-westerly winds increasing. Cloudy. Freezing level rising to around 1300m.
Avalanche Summary
A natural avalanche cycle began on Saturday in response to snow, wind and warming. Some operators reported numerous size 1-3 natural avalanches, starting in the alpine on all aspects. Skier-triggered slabs were also reported in the size 1-2 range, failing on storm snow weaknesses. Previously this week, many avalanches were triggered remotely (from several hundred metres away) and accidentally by skiers and machinery. These avalanches failed on upper snowpack persistent and storm snow weaknesses, on a variety of aspects and elevations.
Snowpack Summary
Snow is falling with strong winds and fluctuating temperatures, creating a perfect recipe for storm slab and wind slab instabilities. This new snow is landing on variable surfaces including surface hoar and facets. Widespread persistent weak layers buried in February have remained touchy all week and are a key concern at all elevations. Storm slabs, wind slabs and sluffs (or you) could trigger these deeper weaknesses, creating avalanches which are larger than you expect, given the amount of fresh snow. Large cornices also loom as potential triggers for deep avalanches.
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.
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.