Touchy and growing storm slabs will keep avalanche danger elevated this week. Riding should be great, but a conservative approach is recommended. Stick to simple terrain.
Confidence
Moderate - Intensity of incoming weather systems is uncertain on Saturday
Weather Forecast
THURSDAY: Periods of snow with 5-10cm of accumulation expected overnight Wednesday and throughout the day Thursday. Freezing levels reaching 1800m with moderate to strong southwesterly ridgetop winds. FRIDAY: A mix of sun and cloud in the morning with light precipitation starting late in the day. Freezing levels reaching 2000m with moderate to strong southwesterly ridgetop winds. SATURDAY: Cloudy with flurries bringing another 5-15cm. Freezing levels steady around 2000m and strong southwesterly ridgetop winds.
Avalanche Summary
Reports from Tuesday include more evidence of the widespread natural storm and wind slab avalanche cycle early Monday primarily in the Monashee Mtns., with avalanches up to Size 3 running on surface hoar buried late February. Continued isolated natural avalanche activity occurred on Tuesday primarily in alpine areas with avalanches observed up to Size 2 in response to loading from fresh snow and wind. Elsewhere, 15-40cm thick fresh storm and wind slabs were highly reactive to human triggers with several direct and remotely triggered avalanches up to Size 2. These fresh storm and wind slabs should increase in size and sensitivity and become much more widespread as they build throughout the week.
Snowpack Summary
10-20cm of fresh snow adds to the now 30-60cm thick storm slabs, which are bonding poorly to on a crust on previously sun-exposed slopes and surface hoar on shady and sheltered slopes. Thicker and touchier wind slabs are lurking throughout exposed terrain at and above treeline. A weak layer of surface hoar and/or a sun crust buried February 21 is now close to a metre below the surface. Where it exists, this layer may become reactive to human triggers as the overlying slab develops. The surface hoar and/or crust layer buried February 10 is likely down over a metre. This layer was less reactive over the weekend with cooler temperatures, but remains a concern for large triggers like cornice falls or a smaller avalanches stepping down. Cornices are large and potentially weak and should be avoided where possible.
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.