We're still managing a midwinter snowpack at and above treeline and the persistent slab problem requires thoughtful terrain selection.
Weather Forecast
The current weather pattern looks more like February than April, but we'll take it! Freezing levels are expected to rise just a bit over the next few days and light daily snowfall should continue through the weekend FRIDAY: Broken cloud cover, freezing level beginning at valley bottom rising to about 800 m, light variable wind, trace of snow possible. SATURDAY: Broken cloud cover, freezing level beginning at valley bottom rising to around 700 m, light variable wind, 1 to 4 cm of snow possible. SUNDAY: Broken cloud cover, freezing level beginning at valley bottom rising to about 1500 m, moderate to strong west wind, 1 to 3 cm of snow possible.
Avalanche Summary
On Wednesday a natural size 3 cornice failure was observed on an unknown aspect, the cornice did not initiate any other avalanche activity. Small loose dry sluffing was also observed on south facing aspects between 1500 and 2100 m suggesting that the cool temperatures are preserving cold snow, even on southerly aspects.Explosives control in the region yielded several persistent slab (size 3) and shallower storm slab (size 1.5) releases on north to northeast aspects in the alpine on Monday. Persistent slabs had 90 cm fracture depths with the shallower storm slabs at 40 cm.
Snowpack Summary
Last week's storms brought 60 to 100 cm of new snow to the region. The snowfall was initially accompanied by strong south winds and then followed by strong north winds, so a mix of old/stubborn and newer, more reactive wind slabs can now be found on a range of aspects at higher elevations. In sheltered areas, this storm snow has been gradually settling into a slab above a persistent weak layer buried in mid-March that consists of crusts at low elevations and on south aspects, and surface hoar on shaded aspects at higher elevations. The structure of storm snow above this layer isn't uniform, however, and recent storm slabs have been observed running on an interface down about 40 cm as well as at the late-March crust. Other persistent weak layers from early January and mid-December are still being reported by local operators, but are generally considered dormant.
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.