Reactive wind slabs can be found on leeward and cross-loaded slopes at upper elevations. Also be mindful of what is above or below you. Cornices may become fragile especially with warming or sun-exposure.
Weather Forecast
SUNDAY: Mostly sunny. Ridge wind light, northeast. Temperature -8. Freezing level valley bottom.MONDAY: Sunny. Ridge wind light, northwest. Temperature --5. Freezing level 800 m. Alpine inversion.TUESDAY: Mostly cloudy, flurries. Accumulation up to 5 cm. Ridge wind moderate, southwest. Temperature -2. Freezing level 800 m. Alpine Inversion.
Avalanche Summary
Saturday a skier triggered a a size 1.5 wind slab release from a cross-loaded feature on a northwest aspect at 1900 m, near Whistler.On Friday, evidence of a natural cycle which likely occurred near the end of the warming period earlier in the week was reported, with storm slab activity up to size 3 observed on north to east aspects in the Mt Currie area.On Thursday, avalanche control with explosives triggered numerous slab avalanches up to size 2. Cornice releases triggered wind slabs from the slopes below up to size 1.5. With colder temperatures expected this weekend, natural avalanche activity will likely taper off, but human triggering will be possible especially on leeward and cross-loaded slopes.
Snowpack Summary
Snow surfaces vary from aspect to elevation showing crusts, wind pressed and scoured conditions. In the alpine 5-15 cm of recent snow, accompanied by strong winds from the southeast have formed reactive wind slabs up to 30 cm thick in leeward terrain, while wind-protected areas still hold unconsolidated, cold snow. At treeline and below treeline elevations a melt-freeze crust has formed up to 1900 m.On average 180 cm of settled snow now sits on the mid-January crust which generally shows signs of bonding to the overlying snow; however, it has the potential to "wake-up" with a large trigger such as a cornice fall. Below this, the snowpack is thought to be generally strong and well-settled.
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.