A variety of weak layers continue to produce human triggered avalanches. We're still managing a midwinter snowpack that requires thoughtful terrain selection.
Weather Forecast
A seasonably cool weather pattern is expected to stick around for the foreseeable future and it looks like we will pick up a few centimeters of snow every day through the weekend too. THURSDAY: Scattered cloud cover, freezing level beginning near valley bottom rising to about 1000 m, light variable wind, 1 to 2 cm of snow possible. FRIDAY: Broken cloud cover, freezing level beginning near valley bottom rising to about 1000 m, light southerly wind at treeline, moderate westerly wind at ridgetop, 1 to 2 cm of snow possible. SATURDAY: Broken cloud cover, freezing level beginning near valley bottom rising to about 1000 m, light southerly wind, 1 to 3 cm of snow possible.
Avalanche Summary
On Tuesday a small avalanche was triggered by a skier on a northeast facing slope at 2200 m. The size 1 avalanche failed on the late March interface. Control work produced avalanches from size 2 to 3 on north/northeast facing features above 2400 m that likely ran on the late March interface as well.On Saturday a skier triggered a large slab avalanche (size 2.5) on a south aspect at 2600 m. The avalanche failed on a buried sun crust 150-200 cm below the surface. Another large (size 2.5) wind slab released naturally from a steep southeast-facing alpine slope in the St. Mary's area. Explosives control in the northern half of the region produced numerous storm slabs ranging from size 1.5-2.5 at treeline and alpine elevations. Crown fractures ranged from 30-100 cm. All aspects were represented in results, with the majority of activity focused on northeast to northwest aspects in the alpine.
Snowpack Summary
Tuesday night's storm brought up to 8 cm of new snow with very little wind.Storms over the past week brought variable snowfall totals of 20-80 cm to the region, with areas to the south of the region seeing the deepest accumulations. This storm snow sits on a persistent weak layer buried in late March that consist of crusts below 1900 m and on south aspects, and surface hoar on shaded aspects at higher elevations. Other slightly deeper surface hoar/facet layers have been reported on shaded aspects at higher elevations and may be found approximately 40-90 cm below the surface.Deeper persistent weak layers from mid-late February as well as January and December layers, are still being monitored by professional observers, but are generally considered dormant. Facets also linger at the base of the snowpack.
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.
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.