Wind slabs still linger in lee features at higher elevations. Watch for signs of avalanche activity and locally unstable snow, such as whumpfing and shooting cracks.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
WEDNESDAY: Mostly sunny, moderate westerly winds, alpine temperature near -13 C, freezing level below valley bottom.THURSDAY: Partly cloudy, light easterly winds, alpine temperature near -12 C, freezing level below valley bottom.FRIDAY: Mostly sunny with increasing cloudiness, light to moderate southwesterly winds, alpine temperature near -11 C, freezing level below valley bottom.
Avalanche Summary
On Monday, a few small slab avalanches (size 1 to 1.5) were reported on northerly to westerly aspects, triggered by small cornice chunks and skiers. They were 10 to 30 cm deep and in treeline and alpine terrain.Avalanche activity may slow down with a period of cold, clear weather that is expected to persist this week. However, the sun is packing more of a punch as the days get longer and it will warm the snow surface on solar aspects if clear skies prevail. Watch for steep sunny slopes due to the sun’s influence, lee features for reactive wind slabs, and be extra cautious near thin spots and shallow snow pack areas where triggering a deeper weak layer is more likely. There is a lower probability of triggering a deeper layer than in previous weeks, but the consequence would be very high if one was triggered.
Snowpack Summary
Around 50-80 cm of recent snow with strong winds have created wind slabs in direct lee features. On steep solar aspects, a thin sun crust exists. These overly a layer of surface hoar, graupel, and a melt-freeze crust buried mid-February. The melt-freeze crust exists up to 1700 m in elevation.Deeper in the snowpack, a widespread weak layer from mid-December composed of facets, crusts, and surface hoar is 120-160 cm deep. Also, a rain crust with sugary facets buried in late November is near the base of the snowpack. If triggered, these weak layers could produce large, destructive avalanches with high consequences.
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.
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.