Avoid avalanche terrain. Heavy snowfall, rain, and wind will create very dangerous conditions on Sunday.
30-60 cm of snowfall will form thick and reactive storm slabs at higher elevations, with natural avalanches likely during periods of heavy precipitation. Human triggered avalanches are very likely.
Rain falling on snow will rapidly weaken the surface and release wet loose avalanches.
A warm front will bring some intense weather the next few days.
SATURDAY NIGHT: Heavy snowfall with 25-35 cm by the morning, strong southwest wind, freezing level climbing to 1100 m by the morning with treeline temperatures around -1 C.
SUNDAY: Another 20-25 mm of precipitation throughout the day with freezing level climbing from 1100 to 1500 m so wet snow will transition to rain, strong southwest wind, treeline temperatures around +2 C in the afternoon.
MONDAY: The storm continues with another 30-50 mm of precipitation and freezing levels dropping from 1500 to 800 m resulting in rain transitioning back to snow, strong west wind, treeline temperatures around -2 C.
TUESDAY: Mix of sun and cloud, moderate northwest wind, treeline temperatures around -3 C.
No notable avalanche activity has been reported since the last decent storm on Monday. With the sheer amount of precipitation expected on Sunday and Monday we can certainly expect avalanche activity, however there is some uncertainty about the transitions between snow and rain which will impact the exact character of the avalanches (e.g. dry storm slabs vs. wet loose). The greatest danger will be on slopes that accumulate lots of fresh snow before it turns to rain. High alpine terrain in the region may not receive any rain, resulting in enormous amounts of snow and extra dangerous conditions.
The snowpack will undergo rapid changes on Sunday and Monday with transitions between heavy snow to heavy rain and then back to snow. A total of 80 mm of precipitation is possible over this period. Forecasts on Saturday suggest the North Shore mountains could get 25-35 cm of snow before it starts to rain on Sunday morning. Once the rain starts low elevations will get wet saturated snow, while higher elevations will continue to get heavy snowfall with strong wind promoting natural avalanches.
Leading into this storm the upper snowpack has an interesting mix of thin crust layers and some soft faceted snow between 30 to 70 cm deep. While avalanches this weekend are most likely going to fail in fresh storm snow layers, there is a remote possibility for these deeper layers to also become reactive (see the latest video from North Shore Rescue for a picture of the snowpack before the storm).
