Forecast heavy rain will be eroding our snowpack on Thursday as well as promoting loose wet avalanche activity. If freezing levels manage to stay lower than expected, reactive storm slabs will form rapidly at higher elevations.
Heavy precipitation carries the possibility of dragging the snowline farther down than forecast freezing levels suggest. With this possibility comes the chance of snowfall accumulating in high alpine locations on the island. If and where this occurs, reactive storm slabs will form rapidly.
Heavy rain will promote widespread wet loose avalanche activity on Thursday.
Wednesday night: Cloudy with increasingly wet flurries bringing 10-30 cm of new snow above 1500 metres, rain below. Strong to extreme southwest winds.
Thursday: Cloudy with another 20-60 mm of rain. 10-30 cm of high alpine snow possible. Strong to extreme southwest winds. Treeline high temperatures around +3 with freezing levels rising to between 2200-2700 metres.
Friday: A mix of sun and cloud. Light to moderate southwest winds. Treeline high temperatures around -2 with freezing levels returning to about 900 metres.
Saturday: Cloudy with heavy rain; 20-60 mm. Strong to extreme southwest winds. Treeline high temperatures around +5 as freezing levels jump to 3000 metres.
No avalanches have been reported in the region. Forecast heavy rain through Thursday will promote widespread wet loose avalanche activity while unfortunately eroding a lot of our snowpack. Precipitation and warming appear to be tightly linked through Thursdays' event, meaning significant accumulations of new snow are not expected. If freezing levels end up staying lower than expected, reactive new storm slabs could form in the alpine.
Thursday's storm will bring 40-60 mm of precipitation to the region, however much of this will fall as rain. Areas directly adjacent to the west coast of the island might see almost double this amount. As temperatures cool into the end of the day Thursday we could see around 10-20 cm of new snow accumulate over the rain-wetted surface.
These final accumulations of dry snow should bond quite rapidly to the underlying wet grains, however it's expected that small, reactive wind slabs will form in specific wind-loaded features in the lee of ridgecrests and other exposed terrain features in the alpine.
Preliminary investigations into the region's existing snowpack suggest the snowline has reached about 850 metres, but that snowpack depths remain below threshold for avalanches below about 1300 metres and in the entire below treeline elevation band. Alpine snowpack depths are likely approaching 150 or more cm, with that depth tapering dramatically with elevation to about 30-60 cm at treeline.
