Persistent slab avalanches continue to pose a low likelihood, high consequence problem at lower elevations.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
MONDAY NIGHT: Clear, light northeast wind, alpine temperatures drop to -15 C.TUESDAY: Sunny, light southeast wind, alpine high temperatures near -8 C.WEDNESDAY: Cloudy with isolated flurries, trace accumulations, light southeast wind with moderate gusts, alpine high temperatures near -10 C.THURSDAY: Scattered flurries with 5-12 cm of snow, 30-50 km/h southwest wind, alpine high temperatures near -4 C.
Avalanche Summary
On Monday, one small (size 1) skier triggered slab avalanche was reported on an east aspect at 1850 m. A few small (size 1) wind slab avalanches and loose dry sluffs were reported over the weekend.
Snowpack Summary
Sheltered areas have 20-40 cm of low density snow on the surface while exposed terrain has been wind affected. Sun crusts can be found on the surface on south-facing slopes. There are potentially three layers of surface hoar in the upper snowpack. One is down 30-50 cm, another is down 40-80 cm, and the last one is down 80-120 cm. These layers have been most prominent and reactive between 1600 and 1900 m over the past month. The lower portion of the snowpack is generally strong.
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.