The first sustained warmup of spring is finally here. Surface instabilities and cornice hazards should be firmly on your radar as you travel. Expect stability to deteriorate over the day.
Weather Forecast
Monday: Mainly sunny. Light southwest winds. Freezing level to 2100 metres and climbing overnight. Alpine high temperatures around 0.Tuesday: Mainly sunny. Light to moderate southwest winds. Freezing level to 2500 metres with alpine high temperatures around +2. Weak overnight cooling.Wednesday: Sunny. Light west winds. Freezing level to 3100 metres with alipne high temperatures around +4. Weak overnight cooling.
Avalanche Summary
Decreasing traffic in the mountains has limited avalanche observations over the past few days.Reports from Thursday included more evidence of the recent natural avalanche cycle described below, with several additional recent storm and wind slab releases to size 2.5 observed. Sun and wind were identified as prominent triggers.No new avalanches were reported in the Cariboos on Wednesday, but reports from the North Columbias included observations of numerous natural wind slab release from size 1-2 on north through east aspects in the alpine. A skier triggered size 2 storm slab resulted in a near miss. Another recent very large (size 3.5) storm slab was observed to have released on a large, wind-loaded alpine feature. Tuesday's reports included observations of several large (size 2) wind slabs that released naturally as a result of recent strong winds.Reports from just over a week ago showed a pattern of heightened cornice failure activity, with several releases triggering large persistent slabs and wind slabs.Looking forward, a period of increasing warming, full sun, and warm overnight temperatures will be maintaining elevated chances of cornice and loose wet avalanche activity.
Snowpack Summary
About 5-10 cm of new snow has accumulated above a melt freeze crust found on the previous surface on all but north aspects above about 2200 metres. Below it, about 50 cm of settled storm snow covers another supportive crust which shares similar distribution to the upper crust.Within this storm snow there are several different crusts with the shallowest of these (down about 25 cm) now a limited concern after warm temperatures have promoted settlement and bonding in the upper snowpack.With warm daytime temperatures and poor overnight recovery of cold temperatures, there remains some lingering concern around reactivity at the mid-March persistent weak layer in the alpine where it is found 100 to 150 cm deep This buried crust/surface hoar layer may still be capable of producing large avalanches if triggered with a heavy load, such as a cornice collapse.Deeper persistent weak layers from December and January may be starting to become reactive to very large triggers. A recent cornice collapse is believe to have initiated a slab release on an early season layer, 300 cm deep.
Problems
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.
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.
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.