Strong northerly winds have loaded many slopes and potentially re-awakened deeper weak layers. Conservative terrain selection remains critical.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
MONDAY: Sunny with cloudy periods, 15-25 km/h east winds, alpine temperatures around -20.TUESDAY: A mix of sun and cloud., 20-30 km/h northeast winds, alpine temperatures around -20.WEDNESDAY: A mix of sun and cloud, 20-30 km/h northeast winds, alpine temperatures around -15.
Avalanche Summary
On Sunday, several natural wind slabs were observed on all aspects and elevations during the peak of the winds. A skier also remote triggered a 70 cm deep wind slab on southwest-facing slope at treeline. Looking ahead to Monday, expect wind slabs to remain reactive to human triggers. The additional load may also make the persistent slab over the mid-December interface more reactive in thin snowpack areas.
Snowpack Summary
Strong northerly winds have formed thick and touchy wind slabs on leeward and cross-loaded features at all elevations. The 40 to 80 cm of new snow the region received between Christmas and New Years has been wind affected and will settle into a slab on south-facing slopes when the sun comes out on Monday. The mid-December facet/surface hoar interface can be found buried 50-100 cm deep. The interface has been showing signs of gaining strength in thick snowpack areas, but remains a concern in thin snowpack areas throughout the region. The lower snowpack is well bonded and features a thick rain crust near the ground.
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.