Regions
Northwest Coastal.
Rain and rising freezing levels over the next few days will weaken the snowpack and increase the Avalanche Danger.
Confidence
Moderate - Freezing levels are uncertain on Monday
Weather Forecast
On Monday, expect 10-15mm of precipitation with freezing levels climbing from 1600m to 1900m throughout the day. On Tuesday the region will see a mix of sun and cloud with freezing levels shooting to 2800m. Light snowfall is forecast for Wednesday. Ridgetop winds are forecast to remain strong from the southwest for the entire forecast period.
Avalanche Summary
On Saturday explosives control in the Stewart and Ningunsaw areas produced deep persistent and storm slab avalanches in the size 2.5-3 range. While most avalanches observed failed within recent storm layers, a few failed on basal facets in shallow snowpack parts of the region. There was also a recent size 3 natural persistent slab avalanche north of Stewart. This avalanche failed on the January 9th surface hoar.Closer to Terrace, a few recent storm slab avalanches to size 3 were observed between 1200 and 1700m. A skier also triggered a size 1.5 wind slab avalanche on a southwest aspect at 1450m. The skier was not injured.I'm sure there was a decent round of storm slab activity on Sunday in response to new snow and wind.
Snowpack Summary
On Monday continued warm, wet and windy conditions will add mass to recently formed storm slabs. Freezing levels are expected to rise dramatically leaving surfaces at treeline and below saturated by the afternoon. Recent storm accumulations may be especially touchy as they are sitting on a new surface hoar layer that was buried on February 3rd. The January 9th surface hoar/facet layer is down 70-150 cm in most places, and remains a concern, especially with heavy and/or thin-spot triggers. Around the same depth you may also find a surface hoar/facet interface from around New Years. There continues to be a lot of uncertainty regarding the reactivity and distribution of this destructive persistent avalanche problem; however, forecast rain and warm temperatures will increase the likelihood of triggering these layers where they still exist. A conservative approach to mountain travel is still required.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.
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.