Avalanche danger will increase throughout the day as new snow adds to an already weak snowpack. Choose conservative routes and dial back you terrain if you see more than 20 cm of new snow.
A deeper weak layer of surface hoar that was buried in early January may become reactive as loading from snow and wind continues.
Storm slabs will be building throughout the day on Sunday, becoming increasingly reactive as more snow accumulates. This adds to slabs from a midweek storm that have been teetering on a fragile layer of surface hoar. Natural avalanches will be likely at higher elevations on wind loaded slopes, while human triggering is a serious concern at all elevations.
A frontal system arrives Saturday night bringing heavy snow and wind through to Monday night.
SATURDAY NIGHT: Arrival of the frontal system brings 5-15 cm of snow, moderate to strong south wind, treeline temperatures around -4 C.
SUNDAY: Continuing snowfall bringing 10-15 cm of snow during the day bringing 24 hr totals to 15-30 cm, moderate to strong south wind, treeline temperatures around -4 C with freezing levels rising to 1300 m.
MONDAY: Snow continues with another 20-30 cm of new snow bringing the 3 day total to 30-60 cm, moderate to strong south wind, treeline temperatures around -4 C with freezing levels rising to 1500 m.
TUESDAY: Scattered flurries with some sunny breaks throughout the day as the frontal system leaves the region, another 5 cm of snow, light southwest wind, treeline temperatures around -6 C.
On Thursday and Friday there were numerous reports of human triggered avalanches in the fresh storm snow. They were reported on all aspects and elevations, and ranged between size 1-2. The primary failure plan in these avalanches was our latest weak layer of surface hoar from late January that was 20-40 cm deep.
The incoming storm will form touchy slabs, with avalanches likely involving multiple layers of recent snow.
New snow will rapidly accumulate between Saturday night and Tuesday, building thick reactive storm slabs. By Sunday afternoon expect 15-30 cm of new snow, adding to the 30-40 cm of snow from a midweek storm. The older storm snow has been reactive to human traffic the past few days, so there will likely be multiple storm slab weakness in play. The older storm snow sits above a melt-freeze crust in many areas around treeline and below treeline, on a sun crust on steep south-facing slopes, and on large surface hoar in sheltered areas.
There are potentially several more layers of surface hoar in the upper snowpack, with the most notable one down about 50-100 cm. This layer was buried in early January. A couple of crusts surrounded by weak faceted grains are buried deep within the snowpack. The upper layer is 100 to 150 cm deep and the lower one is near the ground.
