The slope testers have been out in full force and we've seen a sharp drop in natural and human triggered avalanche activity since the end of the week. Even so, watch out for lingering wind slabs and keep in mind the potential for large and destructive persistent slab avalanches.
Previous snow and wind have created deep pockets of wind slab in lee terrain features at upper elevations. These were very reactive before the weekend and may remain sensitive to human triggers.
Cornices have also been growing. A cornice fall is a large load that can trigger avalanches on the slope below.
A weak layer of surface hoar that was buried around Christmas is now down about 40-80 cm and is most prevalent at treeline and below. This layer remains at a depth triggerable by skiers, sleds and wind slab avalanches.
A deeper persistent weak layer buried in early/mid-December is now down 90 to 150 cm. Triggering these layers require large loads such as explosives or other avalanches in motion. The result of a step down to these layer would be large and destructive.
Saturday night: Increasing cloud, isolated flurries, light to moderate southeast wind, freezing level valley bottom.
Sunday: Mostly cloudy, moderate southwest wind, alpine high -7, freezing level 600 m.
Monday: Flurries, up to 5 cm, moderate southwest wind, alpine high -6, freezing level 1000 m.
Tuesday: Snow 5-10 cm, strong southwest wind, alpine high -5, freezing level 1200 m.
Avalanche activity during the week was generally large (averaging size 2), a combination of wind and persistent slabs, triggered both naturally and by humans.
Around 40-80 cm of recent snow sits on a weak layer of surface hoar that was buried around Christmas. This layer is most prevalent at and below treeline. Previous moderate to strong winds have redistributed surface snow, creating wind slabs at wind exposed elevations.
A couple of persistent weak layers buried in early/mid-December are down about 90-150 cm. Generally, they can be found as a layer of surface hoar above in close proximity to a crust/surface hoar layer. The form and distribution of these layers are highly variable and conditions may differ significantly from one valley to the next.
