Wind slabs formed early-weekend have been reactive to human traffic. Snowfall on Monday could build new slabs, which may not bond well to variable underlying surfaces.
Confidence
Moderate - Intensity of incoming weather systems is uncertain
Weather Forecast
MONDAY: Cloudy with light snowfall, accumulation 5 to 15 cm, light to moderate southeast winds, alpine temperature -5 C, freezing level 1400 m.TUESDAY: Cloudy with light snowfall, accumulation 2 to 5 cm, light west winds, alpine temperature -6 C, freezing level 1300 m.WEDNESDAY: Mostly cloudy, light southwest winds, alpine temperature -7 C, freezing level 1300 m.
Avalanche Summary
On Saturday, wind slabs and cornices were reactive to explosives, producing small avalanches generally in wind-loaded alpine and treeline terrain.
Snowpack Summary
30 to 40 cm of recent snow has been redistributed by strong south winds, forming reactive wind slabs up to 1 m deep in lee terrain features. Sun, rain, and warm air temperatures on Sunday moistened the snow surface, which will freeze into a melt-freeze crust on all aspects up to at least 1800 m. Snowfall on Monday will fall on these surfaces. Ridgelines are heavily corniced and if they fail they could trigger slabs on slopes below.A weak layer consisting of surface hoar, facets, and/or a melt-freeze crust from late March is now buried about 60 to 140 cm. Although this layer is spotty in its distribution and avalanches haven’t been reported on it since early April, professionals are treating it seriously and avoiding terrain because of it. It is mostly likely to be problematic on west, north, and east aspects between 1900 m and 2250 m.Below this, the snowpack is well-settled and strong.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.