Assess for wind slabs in steep terrain and use caution on southerly slopes if the sun is out.
Wind slabs may be found at higher elevations, particularly in steep terrain adjacent to ridgelines. Slabs may be particularly touchy where they sit on a weak layer of surface hoar crystals.
Mild weather and periods of sun will moisten the snow surface at low elevations and on southerly slopes. Best to avoid steep sun-exposed slopes during the heat of the day. Cornices may also weaken with daytime warming.
Weak, sugary faceted grains exist near the base of the snowpack. Riders are most likely to trigger this layer in steep, rocky slopes where the snowpack is inherently thin. The likelihood of avalanche activity on this layer will increase during periods of rapid change to the snowpack, such as heavy snowfall, rain, or extensive warming. Cornices are also very large at this time of year and a cornice failure could trigger this layer.
A handful of wind slab and storm slab avalanches were reported over the past few days, being triggered naturally, by riders, and by large loads like cornice falls and vehicles. The avalanches were small to large (size 1.5 to 2.5) and releasing within the 20 cm of recent storm snow in alpine terrain near ridge tops.
Looking forward, we expect that riders could continue to trigger wind slabs in lee terrain features at higher elevations. Periods of sun and mild weather will increase the likelihood of loose wet avalanches on sun-exposed slopes and cornice falls.
Around 15 to 25 cm of recent snow overlies large (10 mm) surface hoar crystals in terrain sheltered from the wind, wind-affected snow in wind exposed terrain, and a hard melt-freeze crust on sun-exposed slopes. The wind has been blowing from the southwest, meaning that the deepest and touchiest deposits are likely found in north to east lee terrain features near ridges. Relatively mild weather and sunny skies may moisten the snow surface on sun-exposed slopes and at low elevations.
The middle of the snowpack is strong and contains numerous hard crusts.
The lower snowpack is composed of weak basal facets. The layer is currently dormant but it may become active with any rapid change to the snowpack, such as rapid loading (e.g., heavy snowfall or rain) or prolonged and extensive warming. Avoiding thin and rocky slopes is still recommended. Cornices are also very large and a cornice failure could trigger this basal layer.
Thursday Night
Partly cloudy with no precipitation, 20 km/h south wind, treeline temperature -6 °C.
Friday
Partly cloudy with no precipitation, 20 km/h south wind, treeline temperature -5 °C, freezing level 1100 m.
SaturdayMostly clear skies with no precipitation, 30 km/h southeast wind, treeline temperature -4 °C, freezing level 1200 m.
SundayCloudy with light snowfall, accumulation 1 to 3 cm, 20 to 30 km/h southeast wind, treeline temperature -4 °C, freezing level 1200 m.
More details can be found in the Mountain Weather Forecast.
