Thursday gives us one more day of tiptoeing around our persistent slab problem before an incoming atmospheric river deals it a serious shakedown.
Elevated winds from varying directions have redistributed light new snow amounts into reactive wind slabs on all aspects and into the treeline. These slabs are a hazard in their own right, but are also balancing on a snowpack containing multiple persistent weak layers. Potential exists for a small avalanche in motion to trigger a deeper weak layer.
There are two prominent weak layers in the snowpack right now that are of concern. The first is a layer of surface hoar that was buried last week, and is approximately 25-35 cm deep. The second is a persistent weak layer that is now buried 50-60 cm. Both layers may be reactive to human triggers. Be aware that if the shallower layer is triggered, it may step down to the deeper layer, resulting in a large avalanche.
WEDNESDAY NIGHT: Mainly cloudy. Light to moderate southwest winds.
THURSDAY: Cloudy with scattered flurries bringing a trace to 10 cm of new snow, increasing overnight. Light to moderate southwest winds. Alpine high temperatures around -5.
FRIDAY: Cloudy with continuing snowfall bringing approximately 20 cm of new snow, with overnight amounts bringing new snow totals to 30-40 cm. Precipitation transitioning to rain as high as 1400 metres as temperatures warm over the day to reach around -1 in the alpine. Freezing level rising to about 1600 metres.
SATURDAY: Continuing snowfall bringing 20-25 cm of new snow and 48 hour snow totals to 70-90 cm. Precipitation falling as rain below around 1300 metres. Alpine high temperatures around -1 with freezing levels to 1500 metres.
Observations from Monday showed one small new skier-triggered wind slab at 1950 metres in Ymir bowl. Elevated winds from varying directions have supported further wind slab formation since that time.
There were reports of a size 1 human triggered avalanche, and natural size 2 avalanche on Saturday that released on the persistent weak layer that is down about 50-60 cm.
Light new snow amounts have been redistributed by southerly winds at higher elevations and have buried a thin new layer of surface hoar likely to be found in more sheltered areas.
Including the new snow, collectively 25-35 cm of recent snow sits on another weak layer of surface hoar in many sheltered areas, and on a crust on steep south facing slopes. This layer may be more reactive to human triggers where wind loading has formed a deeper, stiffer slab above it.
Another persistent weak layer found approximately 60-100 cm deep consists of a tightly-spaced series of crusts with sugary faceted snow as well as suface hoar found in between them. This complex layer is more likely to be reactive to human triggers in shallow, rocky areas.
