The snowpack remains complex due to stubborn buried weak layers. Very large, destructive avalanches are still possible. Conservative route selection remains crucial at this time.
Weather Forecast
A weak frontal system should bring light precipitation to the interior midday Saturday but the Cariboos, especially the north, may only see scattered flurries. A ridge of high pressure builds in its wake on Sunday and should persist through Monday. The next system is expected for Tuesday. Saturday: Light precipitation 1-2mm, freezing level am: surface pm: 600m, ridgetop wind light SE-SWSunday: A mix of sun and cloud, dry conditions, freezing level am: surface pm: 900m, ridgetop wind light W-NWMonday: A mix of sun and cloud, dry conditions, freezing level am: surface pm: 1300m, ridgetop wind light S-SW
Avalanche Summary
Reports from Thursday include several natural storm slab avalanches up to size 2 releasing down 30-40cm. Also reported was a natural cornice fall triggering a size 2.5 avalanche which released on the early-February weak layer.Generally, we are still seeing relatively small inputs, like periods of strong winds or brief sunny breaks, trigger deeper persistent slab avalanches. Many of these events have occurred on southerly aspects from slopes in the alpine or at treeline. Extra caution is advised when the sun is out.
Snowpack Summary
Around 30-40cm of recent storm snow fell earlier in the week. There may be a variety of layers within the storm snow including thin sun crusts, graupel balls, and maybe even small surface hoar from brief clearings overnight. Also, expect wind slabs in exposed lee and cross-loaded terrain from recent SW-W winds. This storm slab sits on a layer of surface hoar and/or sun crust. A couple other notable persistent weakness layers remain a concern in the mid-snowpack. The surface hoar/sun crust combo buried in early March is now down around 60-80 cm. The early-February surface hoar/facet/crust combo is down 90-150cm and widespread throughout the region. Smaller avalanches stepping down and cornice falls have the potential to initiate an avalanche on this deeply buried weak layer. The mid and lower snowpack remains weak and facetted in areas with a relatively shallow snowpack.
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.
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.