Regions
Northwest Inland.
Wind slabs have been building at higher elevations: Carefully assess conditions as you travel and be alert to changes in the snowpack.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
We'll have lingering flurries in the wake of the snow from Monday-Tuesday. The next significant weather arrives Friday. WEDNESDAY: Cloudy, sunny breaks and lingering flurries (5cm possible) light southerly wind, freezing levels 1200m, alpine temperature around -4 C.THURSDAY: A short-lived clearing during the day. Light-moderate south wind, freezing level around 1100 m with alpine temperature around -3 C.FRIDAY: Snow throughout the day (5-10cm), moderate southwest wind, freezing levels 1300m.
Avalanche Summary
On Monday, skiers were able to trigger a Size 1 wind slab on a north aspect at 1600m in the north of the region. On Sunday, a Size 2 natural wind slab (average depth 40cm) was reported on a northeast aspect near 1800m in the south of the region.On Saturday, several wind slabs to Size 1.5 were reported on (east) northeast aspects in the north of the region.The incoming weather will continue to add load to the persistent slab, and human triggering remains possible in steep or unsupported terrain.
Snowpack Summary
Variable and unsettled weather has given 5-20cm of new snow in the past few days. Winds have been moderate to STRONG south though westerly, and many exposed surfaces are either heavily scoured or wind-pressed firm. That said, there have been some reports of wind slabs forming on northeast aspects in the south of the region. Recent warming and sun have likely left a crust on solar aspects and below 1300 m (reportedly breakable crust below 1000m). Snow from the past week or so has settled into a 20-60 cm thick slab above an older crust interface. Reports suggest the bond to the crust is poor and has resulted in a reactive slab, in addition to weaknesses down 30-35cm within the storm snow itself (giving sudden planar results in snowpack tests).Weak sugary snow near the ground has been a dormant instability, but it may still be possible to trigger in steep rocky terrain.
Problems
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.
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.