Don't be too quick to rule out the storm slab problem. That heap of new snow sits on a questionable interface and more is on tap for Sunday night. Use low consequence slopes to assess the new snow's bond and raise your guard as you approach exposed terrain where new wind slabs present a more certain hazard.
With 20-40 cm of new snow from Saturday overlying weak grains like faceted snow and small surface hoar, we may see storm slab reactivity persist for longer than usual. What's more certain is that large wind slabs perched on leeward (north-facing) terrain will be primed for human triggering.
A weak layer of facets exists near the base of the snowpack. The likelihood of human triggering is low given the layer's deep burial depth, but storm slab avalanches in motion have the potential to step down. Suspect terrain for human triggering includes steep, thin, shallow, and rocky terrain, which is often found near ridgelines.
Observations of new avalanche activity from Saturday and Sunday are still limited to reports from the early hours of the storm when a small storm slab problem began to take shape. We anticipate some degree of a natural avalanche cycle has since place throughout the region but especially where 30 cm or more new snow accumulated.
On Friday, we received reports of many natural, explosive, and human-triggered storm slab and wind slab avalanches from all aspects. The majority of this activity occurred at treeline and in the alpine, and was typically around size 2 with a few up to size 3. The typical release depth of these avalanches varied from 20 to 60 cm.
Clear skies a few days ago allowed for observations of many deep persistent slab avalanches as well as explosive control missions, which produced large to very large (size 2 to 3.5) avalanches. They were on all aspects and between 2200 m and 2800 m in elevation. Although many of the avalanches occurred in unrideable terrain, they are evidence that the weak basal snowpack is still triggerable. Riders should continue to avoid thin snowpack areas, which are often found near ridgelines.
Stormy conditions brought up to about 40 cm of new snow to the region along with strong southwest wind on Saturday. The new snow buried an interface from the recent cold period which includes faceted (sugary) surface snow, small surface hoar in sheltered areas, and widespread heavy wind effect and wind slabs in exposed terrain from recent northeast winds. Below this interface is 20-50 cm of older storm snow from the beginning of last week.
Around 80 to 100 cm of snow may rest on a small layer of surface hoar crystals that was buried mid-February. This layer is most likely found around treeline elevations in areas sheltered from the wind. This layer generally appears to be dormant now but could still be capable of producing avalanches in isolated areas. The remainder of the mid-snowpack is generally strong.
A layer of large and weak facets that formed in November is deeply buried, found near the base of the snowpack. The likelihood of human triggering this layer is currently low given its depth. However, it is still best to avoid steep, thin, rocky slopes near ridges at alpine and upper treeline elevations.
Sunday night
A final round of convective flurries bringing up to about 5 cm of new snow. Light to moderate southwest winds easing into the morning.
Monday
Mainly cloudy with isolated flurries. Light south winds. Treeline high temperatures around -9 °C.
Tuesday
Mainly cloudy with isolated flurries. Light east or southeast winds. Treeline high temperatures around -8 °C.
Wednesday
Mainly cloudy with isolated flurries. Light west winds. Treeline high temperatures around -8.
More details can be found in the Mountain Weather Forecast.
