Regions
South Coast Inland.
A spike in natural avalanche activity may occur due to strong solar effect.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
The weather pattern has taken a dramatic shift as the arctic ridge becomes the dominant weather feature through the weekend, bringing colder temperatures and mostly clear skies.Saturday: Mostly clear skies. Alpine temperatures near -2 and freezing levels 1100 m. Ridgetop winds light from the West. Sunday: A mix of sun and cloud. Alpine temperatures near -7 and freezing levels 800 m. Ridgetop winds light from the northwest.Monday: Mostly sunny. Alpine temperatures near -10 and freezing levels 600 m. Ridgetop winds light from the northeast.
Avalanche Summary
On Thursday, the southern part of the region reported a natural slab avalanche size 3.5 from a NE-SE aspect near 1800 m and numerous wet slabs up to size 2.5. An avalanche control mission using explosives in the northern part of the region saw wind slab results up to size 1.5, only running in the surface snow and not stepping down deeper.
Snowpack Summary
Recent snowfall totals are highly variable. In the south, up to 40 cm of new snow fell bringing the alpine totals up to 60 cm this week. In the north, new snow totals are half that and rapidly decreasing below 1800m. This new snow sits on old wind slabs in alpine locations and has buried a crust at treeline. At lower treeline and below elevations, warm temperatures and rain have saturated the upper snowpack. A solid surface crust will likely form with forecast cooler temperatures.Below the surface, 80-150 cm down in the mid pack sits the mid- January crust. It generally shows signs of bonding to the overlying snow; however, I would remain suspect of this deeper layer while the snowpack adjusts to the new load. Thinner snowpack areas may have a higher likelihood of an avalanche failing on this layer. Large, looming cornices exist, they are fragile and demand respect.
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.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.