A shallow snowpack, deep persistent slab and basal weakness have created a tricky start to the season - conservative route selection and avoidance of big terrain in the alpine is advised. Have a safe and happy holiday season!
Weather Forecast
Mild temperatures through to Friday evening, at which point they are expected to drop back to more seasonal norms (-10C at 2100m). Southwest flow will continue to dominate with generally light to moderate values, gusting to high in the alpine. Minimal precipitation is expected - models predict 0-5cm over the next 24 hours. Freezing level 1400m.
Snowpack Summary
No significant precipitation over the last week (1mm in past 72 hours / 5mm past 7 days). Snowpack is generally shallow, weak, with a variably distributed deep persistent slab overlying weak basal layers of depth hoar, crusts, and/or facets. A steady southwest flow has created pockets of windslab in exposed areas at treeline and above.
Avalanche Summary
1 new natural slab avalanche observed today in the alpine on a Southwest aspect - size 2. Likely ran on basal weakness. Numerous natural slab avalanches to size 2.5 observed in the past week, primarily on cross loaded gully features in the alpine.
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.