Spring is a tricky time. Heat-related cornice and wet loose problems rise and fall each day, but deeper snowpack weaknesses remain in play. Use conservative terrain to manage uncertainty.
A weak layer of facets and/or surface hoar is buried 50 to 100 cm deep. It is most prominent on terrain features sheltered from the wind. Where this layer exists, it remains possible for the weight of a person or machine to trigger it.
Wet loose avalanches are likely in steep terrain during the heat of the day. Cornices also weaken and could release naturally. These could step down to deeper layers, forming large avalanches.
A large (size 2) loose wet avalanche triggered a slab about 50 cm deep on Tuesday at 1700 m. It is possible that it triggered the weak layer described in the snowpack summary.
Otherwise, the most recent persistent slab activity was a week ago. Although likelihood is decreasing, it remains possible for humans to trigger this buried weak layer.
Also expect sun-exposed slopes to become unstable with daytime warming, possibly triggering wet avalanches or releasing cornices.
Dry, settled snow is found on shaded aspects in the alpine. A hard melt-freeze crust exists on the snow surface on sun-exposed slopes to the mountain tops and on all aspects below treeline. The crust will transition to wet snow with daytime warming and re-freeze at night.
50 to 100 cm of snow overlies a hard melt-freeze crust from early April. The overlying snow is slow to bond to the crust where pockets of weak surface hoar or faceted grains rest on the crust, which is most likely on northerly aspects at treeline and alpine elevations.
Thursday night
Clear skies. 20 km/h east ridgetop wind. Treeline temperature around +1 °C. Freezing level rising to 1800 m.
Friday
Clear skies. 20 to 30 km/h east ridgetop wind, increasing. Treeline temperature 0 °C. Freezing level to 1500 m.
Saturday
Clear skies with cloud invading late afternoon. 20 to 30 km/h southeast ridgetop wind. Treeline temperature 0 °C. Freezing level to 1500 m.
Sunday
Increasing cloud with isolated flurries in the afternoon. 10 - 15 km/h southwest ridgetop wind. Treeline temperature 0 °C. Freezing level to 1500 m.
More details can be found in the Mountain Weather Forecast.
