Stormy conditions continue on Sunday in the south of the region. Tricky conditions are expected in the alpine and conservative decision making is essential.
Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
Variable conditions are expected for Sunday across the region. A ridge of high pressure building over central BC should keep the north of the region mainly dry. A storm system will track south of the US border on Sunday and should bring light to moderate precipitation to the southern half of the region. Freezing levels on Sunday are expected be around 1500m and alpine winds should be moderate from variable directions. On Monday, the north of the region should stay mainly dry but the south of the region may see lingering precipitation. WInds should be light and freezing levels around 1500m. Tuesday looks to be unsettled and freezing levels may reach over 2000m.
Avalanche Summary
On Friday, numerous loose wet avalanches up to size 2 were reported from solar aspect slopes. On Thursday, a cornice failure triggered a small wind slab on the slope below and a natural size 2 slab was reported from a steep rocky sun-exposed slope. During the last few days there have been some concerning avalanches in the neighboring Columbia regions including natural slabs releasing to ground and very reactive wind slabs over facets being remotely triggered. On Sunday, touchy wind slabs are expected in the alpine and loose wet sluffing is possible from steep slopes at lower elevations. There is a still a concern for avalanches to step down to deeply buried weak layers resulting in larger persistent slab avalanches.
Snowpack Summary
At higher elevations, new snow sits over a variety of surfaces including moist snow, crusts, wind affected surfaces, and/or old wind slabs which may still be reactive. Rain has soaked the upper snowpack to around treeline elevation. In the alpine, strong winds during the storm are redistributing the new snow into wind slabs in leeward terrain features. Prior to the storm, 10-30cm of snow was sitting over a weak facet/crust layer that was buried in mid-February. The late-Jan crust/surface hoar layer can be found around 1m below the surface in deeper snowpack areas. The mid-January surface hoar can be found below that. These layers have gained significant strength and have been dormant for several weeks but have the potential to wake-up with the current warm temperatures and loading.
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.
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
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.