New snow followed by heavy rain is Tuesday's recipe for rapidly changing and dangerous avalanche conditions.
Forecast weather suggests a storm slab problem could form with new snow before precipitation switches to rain at all elevations on Tuesday. Any fresh accumulations will shed from steep slopes increasingly easily as temperatures rise.
New snow followed by a deluge of rain will breathe new life into wet loose avalanche problems on Tuesday. The more new snow has accumulated before the transition to rain occurs, the greater the danger will be.
Monday night: Cloudy with flurries bringing 10-15 cm of new snow. Strong southwest winds.
Tuesday: Moderate snowfall switching to heavy rain by about noon; 15-35mm over the day and increasing overnight. Strong to extreme southwest winds. Treeline temperatures rising from 0 to +5 as freezing levels climb from 1400 to 3000 metres.
Wednesday: Continuing heavy rain switching to light snowfall late in the afternoon. Minimal accumulation. Strong southwest winds easing over the day. Treeline temperatures dropping from about +4 to 0C over the day as freezing levels return to about 1500 metres.
Thursday: Clearing. Light west winds. treeline high temperatures around -5.
Looking forward to Tuesday, new snow accumulations from overnight and the early part of the day will be impacted by heavy rain. This should set up a rapidly changing risk scenario where a building storm slab problem transitions to active wet loose avalanche conditions over the day.
Heavy rain has affected the snowpack at all elevations. Surface crusts have likely formed at all but the lowest elevations holding snow cover. Forecast weather should add brief new snow accumulations before heavy rain drenches the snowpack once again.
Early indications of our region's existing (but eroding) snowpack suggest alpine snowpack depths around 150 cm, depth tapering dramatically with elevation to about 30-60 cm at treeline. Snow cover is thin and generally below threshold for avalanches below about 1300 metres.
