Winds are building slabs along ridgelines and in lee terrain features, expect more rapid development as wind increases.
Increasing winds impacting 10-30 cm of soft surface snow may blow into unstable slabs. Where the new snow overlies surface hoar (or a crust) a poor bond has been noted, and reactively will increase where soft snow gains cohesion and slab properties.
The problem is more likely found in northern parts of the region (e.g. Golden).
A facet/crust layer from early November sits near the base of the snowpack. This layer has shown signs of recent reactivity with explosive control in shallow rocky locations producing large avalanches. It is most likely to be triggered by humans in shallow, rocky areas or in a step-down from a smaller avalanche.
THURSDAY NIGHT- Mainly cloudy with isolated flurries. trace to 5 cm / west wind, 20-50 km/h / alpine high temperature near -6
FRIDAY - Mainly cloudy with scattered flurries, trace to 10 cm / southwest wind, 20-40 km/h / alpine high temperature near -8
SATURDAY - Mainly cloudy with scattered flurries, 10 cm / southwest wind, 25-55 km/h / alpine high temperature near -6
SUNDAY - Snow, 10-20 cm / southwest wind, 20 gusting to 80 km/h / alpine high temperature near -1 / Freezing level rising to 1700 m
Moderate southwest winds may form fresh windslabs that could be reactive to human triggers at upper elevations. Check out this MIN report from the KHMR backcountry - poor bonding between the new snow and old surface resulting in sluffing and loose, dry avalanches, and small windslabs in steep rocky terrain.
Avalanche control work on Tuesday produced a few small (size 1) storm slab and dry loose avalanches.
A MIN report from the Clamshell near Golden reported a natural size 2.5 avalanche last Wednesday (Dec 9). This avalanche appears to have run on a weak layer roughly 40 cm below the surface, which seems to be an isolated problem in this area.
15-25 cm of snow overlies a rain crust found up to 2400 m in the south of the region and 1800 m in the north, the recent snow may sit over a weak layer of surface hoar or facets at elevations around treeline where this crust is not found. South-southwesterly winds are creating new, small cornices and wind slabs on lee slopes. The recent snow may not be bonding well to older surfaces. There have also been some reports of an isolated weak layer 40 cm below the surface around Golden.
The lower snowpack is characterized by a couple of crusts, the most notable is from a rain event in early November that is 50 to 100 cm deep. This crust is sitting near the base of the snowpack, surrounded by a weak layer of sugary facets. It is most likely to be reactive to human triggers or in a step-down from a smaller avalanche in shallow, rocky areas.
