Regions
Northwest Inland.
Benign weather this week. Watch for isolated wind slabs and shallow snowpack areas where triggering a deep persistent slab avalanche remains possible.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
MONDAY: Isolated flurries with trace accumulations, light south winds, alpine temperatures around -8 C.TUESDAY: Cloudy with sunny periods, light northwest winds, alpine temperatures around -10 C.MONDAY: Mix of sun and cloud, light northwest winds, alpine temperatures around -12 C.
Avalanche Summary
On Saturday, numerous small natural wind slabs (size 1-1.5) were reported on northwest aspects around treeline. Small loose dry avalanches running above the rain crust were reported in steep terrain. Watch for isolated pockets where thicker wind slabs could produce larger avalanches. Also keep in mind that a basal weakness continues to drive a low probability/high consequence avalanche problem for the region. Very large avalanches remain possible, especially in shallow snowpack areas.
Snowpack Summary
Clear cold weather and shifting winds have created a variety of surface conditions including isolated wind slabs, pockets of soft snow (5-10 cm deep), sun crusts, and surface hoar. A supportive rain crust exists below 1000 m. A layer of surface hoar that was buried on February 10th may exist 30-60 cm below the surface, but there's a fair bit of uncertainty regarding the reactivity and distribution of this layer. A stiff mid pack sits above weak sugary snow near the ground. Although possibly dormant, this basal weakness has the potential to produce very large destructive avalanches.
Problems
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.
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.