Warming will seriously test the snowpack in the coming days and will likely produce destructive persistent slab avalanches. It might feel like spring, but the snowpack is far from settled.
Weak layers exist below the most recent storm snow and up to about 60 cm deep. They will be increasingly likely to produce avalanches with forecast warming. Small avalanches may also step down.
A mix of natural, remotely tiggered, and ski cut avalanches in the size 1 - 1.5 range were observed Tuesday, involving both the recent storm interface and deeper persistent weak layers. Visibility was limited, so the full extent of activity isn't certain.
Avalanches reached size 3.5 on Monday, with natural releases during periods of heavy snowfall and strong winds.
Activity of this type is expected to resume or even intensify as forecast warming tests the snowpack.
By Thursday, a new melt-freeze crust should glaze the surface on solar aspects and below about 1700 m. The depth of affected snow should increase over the coming days and crust recovery may be weak. This process will affect 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 as forecast warming tests the snowpack.
Wednesday night
Mostly clear skies with possible valley cloud. 20 to 30 km/h southwest ridgetop winds, increasing. Treeline temperature -3 °C. Freezing level 1400 m with a possible above freezing layer around 2500 m.
Thursday
Mostly sunny with possible valley cloud. 20 to 30 km/h southwest ridgetop winds. Treeline temperature +4 °C. Freezing level rising to 2200 m, higher overnight.
Friday
Sunny. 10 to 20 km/h southwest ridgetop winds. Treeline temperature +5 °C. Freezing level rising to 2500 m.
Saturday
Sunny. 20 km/h southwest ridgetop wind. Treeline temperature +6 °C. Freezing level 2800 m.
More details can be found in the Mountain Weather Forecast.
