With so much uncertainty about tonight's rain vs. snow battle, your validation of conditions on the ground is key. Expect dangerous avalanche conditions where 30 cm or more accumulates.
Heavy snowfall and high winds will rapidly form storm slabs at high elevations in the coming storm. Warm temperatures and rain will promote a natural avalanche cycle.
Rain on fresh accumulations of wet, heavy snow will drive wet loose avalanche conditions at mid elevations, and possibly even in the alpine.
Unsurprisingly, no new or even recent avalanches have been reported on the Island during the extended snowfall drought.
The Friday Night to Saturday storm is set to change the scene dramatically, at least in the alpine, where heavy snowfall is expected to perpetuate a natural avalanche cycle. Treeline is a lot more uncertain.
By end-of-day Saturday, a highly uncertain 40 to 80 cm of new snow might accumulate in the alpine. Accumulations will taper sharply with elevation, leaving treeline elevations especially uncertain. Heavy rain will mostly fall on vegetation below treeline.
Where snow accumulates, it will bury a widespread, moist or wet crust over a thoroughly settled, recently isothermal snowpack. It's still about a metre deep in the alpine, but becomes patchy and disconnected at treeline. There is very little snow below treeline.
Friday Night
Cloudy with increasing snowfall bringing 20 to 30 cm of alpine snow, tapering to rain below about 1400 to 1600 m. 40 to 70 km/h south ridgetop wind, increasing. Treeline temperature 3 °C. Freezing level 1700 to 1900 m.
Saturday
Cloudy with continuing heavy precipitation bringing 25 to 50 cm of alpine snow, tapering to rain below about 1500 to 1700 m. 40 to 70 km/h southwest ridgetop wind, easing. Treeline temperature 4 °C. Freezing level 1800 - 2000 m.
Sunday
A mix of sun and clouds with isolated flurries. 10 to 20 km/h southwest ridgetop wind. Treeline temperature 0 °C. Freezing level 1300 m.
Monday
Mostly cloudy with scattered flurries bringing 5 - 10 cm of new snow. 20 km/h southwest ridgetop wind. Treeline temperature -1 °C. Freezing level falling to 1000 m.
More details can be found in the Mountain Weather Forecast.
