Central Sierra Nevada

A small avalanche was unintentionally skier triggered yesterday mid slope in below treeline terrain.  On a regional scale, avalanche activity remains unlikely. Keep your guard up and use best practices for travel in avalanche terrain in order to minimize the consequences of encountering isolated, unexpected areas of unstable snow. This is the continuation of a 48 hr forecast published Dec 24 with the next update occurring on Dec 26.

Normal caution

Read the details here on the shallow, size D1 avalanche with wide propagation that was triggered yesterday mid slope in below treeline terrain around 8,500' on the NE aspect slopes of Ralston Peak. While slab depth was just 4 to 6 inches max depth, this avalanche potentially failed on the buried surface hoar that we have been monitoring. Avalanche activity remains unlikely for today on a regional scale. This is a prime example of the type of isolated instability that often occurs during LOW danger. Use normal caution and employ best practices for travel in avalanche terrain in order to minimize the consequences of unexpected encounters with isolated areas of unstable snow.

At 4 to 6 inches max slab depth, this is by far the most snow reported on top of this particular buried weak layer. In most areas, the surface hoar is buried less than one inch below the snow surface. This buried surface hoar layer will likely become less widespread as a concerning weak layer following the warm temperatures of today and tomorrow. To what extent it remains as a weak layer in isolated distribution or greater going into the next storm cycle is an open question at this time.

While we are in a significant warming period, wet snow instability beyond minor surface instabilities such as rollerballs and small pinwheels is unlikely.

Recent Observations:

• Surface hoar commonly buried less than an inch below the snow surface appears most prevalent across NW-N-NE aspects on the low to upper mid slope portions of any given terrain rather than within a specific elevation band. It has been observed below treeline in many openings larger than about 30 feet across.
• Warming temperatures, dripping trees, and tree bombs have formed variable snow surface conditions.  Wet snow now exists on most aspects at low and mid elevations due to the recent warm and at times cloudy conditions.
• Rollerball activity has been prominent on northerly aspects as previously cold dry snow becomes wet. This has mostly been an issue below about 8,000' to 8,500'. It may spread to higher elevations as warming continues.