Skyrocketing alpine temperatures and reactive persistent slabs are a bad mix. Saturday will be a day to avoid avalanche terrain entirely, no matter how enticing it looks.
Weak layers exist below the most recent storm snow and up to about 90 cm deep. They will be increasingly likely to produce avalanches during the warmup. Small avalanches may also step down.
High freezing levels and solar warming will work to destabilize snow on steep slopes sheltered from the wind. Moist or wet snow may shed naturally or with a human trigger and loose releases may trigger more destructive slab avalanches.
A final 10 - 20 cm of new snow led to active avalanche conditions in the midweek, with a variety of triggers producing mainly small storm and wind slab releases. These ranged from 10 - 40 cm in depth while recent persistent slabs in the size 2 to 3.5 range, predominantly running on the late January crust, have featured 60 - 80 cm crowns. See the size 3.5 below. Persistent slab activity in particular is expected to resume or possibly intensify as warming tests the snowpack.
A melt-freeze crust or moist snow now glazes the surface on solar aspects and, by Saturday, as high as mountaintop. High overnight freezing levels mean crust recovery may be weak. This process is affecting the upper part of 30 to 50 cm of settling recent snow, which is wind affected at higher elevations and may overlie faceted snow or surface hoar where sheltered.
Two other key weak layers are present in the mid snowpack: a surface hoar or thin crust from mid-February buried 40-60 cm deep, and faceted snow/surface hoar/crust from late January buried 60-90 cm deep. These layers have been active during recent storms and are expected to produce avalanches while warming tests the snowpack.
Friday Night
Clearing. 10 to 15 km/h southwest ridgetop winds. Freezing level rising to 2500 m.
Saturday
Sunny. 15 to 20 km/h southwest ridgetop wind. Freezing level to 3100 m. Treeline temperature 7 °C.
Sunday
Mainly sunny with cloud increasing. 10 to 15 km/h variable ridgetop wind. Freezing level falling from 2700 m to 2400 m. Treeline temperature 6 °C.
Monday
A mix of sun and cloud. 10 to 20 km/h northeast ridgetop wind. Freezing level to 1800 m. Treeline temperature 3 °C.
More details can be found in the Mountain Weather Forecast.
