Avalanche Forecast

Archived

Dec 30th, 2018–Dec 31st, 2018

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

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Stubborn wind slabs exist in unusual locations including well below ridgeline and on the sides of mid-slope gullies. You can use visual clues like the snow blown off trees, new snow drifts, and fresh cornices to show you wind slabs are nearby. In some locations wind transported snow may sit on a layer of buried surface hoar. If you trigger a wind slab in these location, it may act in surprising ways and propagate widely.

Discussion

Avalanche and Snowpack Discussion

On Sunday, several avalanches were reported from the south side of Mt Baker and Heather Meadows. Most of these avalanches likely occurred during heavy precipitation Saturday. Some of these avalanches were unusual. They occurred mid-slope, propagated widely, had shallow crowns, and/or occurred in small openings in the trees. When we see signs like this, it suggest a buried persistent weak layer. A layer of buried surface hoar was found in snow profiles nearby.

12/30/18: Slab avalanches from Saturday’s storm. Many of these failed on a layer of buried surface hoar and propagated widely. Photo: Andrew Kiefer

We removed the deep persistent slab from our avalanche problem list. It has been more than a week since our last reported avalanche on this layer. Given its depth and the lack of activity, we believe this layer is very unlikely to produce new avalanches. We will continue to monitor this weak old snow, and update you if we find any new information.

Snowpack Discussion

Updated Regional Synopsis coming Sunday 12/30

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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.