An overnight transition from rain to snow leaves us with some uncertainty for Wednesday. Expect the new snow to form touchy slabs in areas where it accumulates.
Confidence
Moderate - Forecast snowfall amounts are uncertain
Weather Forecast
Tuesday night: Rain transitioning to wet flurries and bringing around 6 cm of new snow. Light south winds.Wednesday: Continuing flurries bringing about 5 cm of new snow. Light southwest winds. Freezing level to 1200 metres with alpine high temperatures of -4.Thursday: Mainly sunny. Light northeast winds. Freezing level to 1400 metres with alpine high temperatures around -5.Friday: A mix of sun and cloud. Light north winds. Freezing level to 1600 metres with alpine high temperatures around -3.
Avalanche Summary
Reports from Monday included observations of three natural size 2.5 loose wet avalanches that released from steep, rocky, south-facing slopes in the afternoon in the Whistler area.On Sunday there was a report of a skier triggered size 2 storm slab avalanche on a west aspect at 2400m. On Saturday there were several size 2.5 natural persistent slab avalanches reported. These were suspected to have run in the previous 24hours and were observed on northwest to east aspects between 1900 and 2000m. Additionally there have been several observations of skier triggered storm and wind slab avalanche size 1-2 mostly on northerly aspects between 1800 and 2000m.
Snowpack Summary
After a bout of light rain, light new snow amounts are expected to accumulate on the surface over Tuesday night and Wednesday. The new snow is accumulating above variable crust and moist snow that formed on the surface after days of warm temperatures and sunshine. The storm snow beneath this interface was previously redistributed by west and south winds.Last week's storms buried a weak layer composed of soft facets, surface hoar, and/or crust that is roughly 50-100 cm below the surface. This layer has produced whumpfing, sudden results in snowpack tests, and some remotely triggered avalanches. Lots of the activity has been on buried surface hoar on north aspects at upper treeline elevations. The snowpack is well settled and strong beneath this interface. Variable winds in the past month have built up cornices on many ridgelines. They will become touchier as temperatures rise and when they are subject to the strong late-winter sun on clear days.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.