Friday is probably the last reasonable day for a big objective for the foreseeable future, as a significant warm up is expected Saturday. The odd wind slab in the alpine may still be sensitive to human triggering.
Weather Forecast
Temperatures are expected to be on the cooler side again Friday before the big wave of warmth crashes into the region Saturday morning. FRIDAY: Freezing level starting at 1400 m, topping out at 1800 m, light to moderate southwest wind, no significant precipitation expected. SATURDAY: Freezing level beginning around 1500 m, climbing to around 2500 m in the afternoon, no significant precipitation, light variable winds at and below treeline, moderate southwest wind at ridgetop. SUNDAY: Freezing level beginning near 2800 m, rising to around 3500 m by the afternoon, no significant precipitation, moderate southwest wind.
Avalanche Summary
In the neighboring Sea-2-Sky region, small storm slab avalanches to size 1.5 were reported from upper elevations Wednesday. (No new avalanches were reported in this region on Tuesday or Wednesday.)
Snowpack Summary
Cornices are large, fragile, and could trigger deep slab avalanches that run to valley bottoms. Monitoring the overnight freeze of the snow surface is very important during the spring. If the snow surface does not freeze overnight or if the crust is only a few cm thick, the effect of daytime heating and solar radiation will weaken the snowpack much more quickly than it would if there is a well frozen thick crust. This is because the crust must first melt before the sun can weaken the snowpack. There is an old crust layer down approximately 50cm in the Duffey area and north of Pemberton. This layer has generally been dormant but resulted in a couple large avalanches during the last major warming event and produced a couple explosive triggered avalanches on Thursday. With continued warming, this layer could wake-up in isolated locations such as steep, rocky faces. Glide cracks are widespread, active, and best avoided. Low elevation and thin snowpack areas have become isothermal, meaning the snowpack is 0 degrees Celsius throughout. An isothermal snowpack is more prone to full depth wet slab avalanches during the heat of the day, especially on steep, rocky faces.
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.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
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.