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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

Two skier triggered avalanches were reported in the Crystal backcountry Sunday. One avalanche occurred in the Cache Creek area on a WNW aspect at 6500 ft. The group was making their second run on the slope when the avalanche occurred. The avalanche was about foot deep, 125 feet wide, and ran 300-400 ft down the slope. No one was injured in the avalanche. Several pieces of this avalanche unusual. It occurred on a relatively low angle (32 degree) treed slope, well below ridgeline. We do not know the weak layer in this particular incident, but information like this suggest buried surface hoar.

We have received reports from Crystal Ski Patrol of buried surface hoar about 1-2 ft below the snow surface on slopes above 6000 ft. Information about the distribution of this layer is limited at this time.

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.