Regions
Kootenay Boundary.
Freezing levels skyrocket to the moon on Thursday. Watch out for failing cornices and expect a widespread loose wet avalanche cycle on solar aspects in the alpine.
Weather Forecast
THURSDAY: Freezing levels skyrocket to 3500m, sunny, light southwest ridgetop winds. FRIDAY: Freezing level 3500m, sunny, light southwest ridgetop winds. SATURDAY: Freezing level 3000m, sunny, light southwest ridgetop winds.
Avalanche Summary
No new avalanches were reported in this region on Tuesday. However, I expect to see widespread natural avalanche activity on Thursday when the recent storm snow is heated by solar radiation and soaring freezing levels.
Snowpack Summary
Large cornices overhang alpine slopes and may trigger large, destructive avalanches running to valley bottoms. Up to 20cm of recent storm snow with moderate northwesterly winds will have created wind slabs on lee aspects in the alpine and open treeline. These wind slabs will increase in sensitivity when they are warmed up for the first time by solar radiation and rising freezing levels. The late February surface hoar/ crust interface down 80 to 130 cm. is currently dormant, however, a rapid warm up could awaken this sleeping dragon. At low elevations, the snowpack is isothermal.
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.