Sea To Sky

It's still winter at treeline and alpine elevations!

Moderate - Due to the number of field observations

TUESDAY: Wake up to 5 to 10 cm of new snow, but only a trace more during the day. Mix of sun and clouds. Treeline temperatures a few degrees either side of zero and alpine temperatures a few degrees below zero.  Freezing level around 1600 m. Light southeast winds.WEDNESDAY:  Mix of sun and clouds. Possibility of traces of new snow in flurries. Freezing level around 1500m with temperatures within a few degrees of zero at treeline and alpine elevations. Moderate southeast winds.THURSDAY:  Cloudy. Flurries with around 5 cm of new snow. Freezing level near 1400 m with alpine temperatures up to -2C. Light southerly wind.

Shallow wind slabs in alpine terrain is representative of the ongoing wind slab concern: localized pockets, lee and cross-loaded features, around 20 to 40 cm thick. Saturday's fatal avalanche accident on Mt. Harvey, although not in the Sea To Sky region, does highlight several of the risks posed by cornices: multi-ton snow boulders serve as large triggers potentially releasing large avalanches on the slopes below, they can break well back making for tricky travel along ridge crests. It's all the more tricky when visibility is obscured in fog or heavy snow, if the easiest pathway (flat, hard snow, open straight line) is within the danger zone, or when they're so big that you need to be 10 or 15 or more metres back from the edge to remain safe. There were two reports of size 3 Cornice triggered avalanches from the Whistler backcountry on Sunday as well as a widespread avalanche cycle to size 3 in the Tanatalus Range, likely releasing on Friday and Saturday during the previous storm.

Recent snow in the last few days built wind slabs, primarily on northerly aspects at alpine and treeline elevations. They should stabilize quickly with warm temperatures but isolated wind slabs behind ridges and similar terrain may linger. Expect multiple crusts in the upper snowpack, especially on southerly facing (sunny) slopes. Thin crusts with facets above are possible making southerly aspects complex and harder to forecast. Cornices are large and remain a concern: yesterday's fatal accident near Lions Bay illustrates the danger of them breaking off, and the large avalanches they can trigger. Sunshine and solar radiation can quickly weaken snow on solar facing slopes.