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Avalanche Forecast

Archived

Dec 19th, 2016–Dec 20th, 2016

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Lizard-Flathead.

I'd give the new snow a few days to settle and gain strength before pushing into any steep terrain. A freshly buried weak layer may prolong the reactivity of newly developed slabs.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Tuesday: 8-15cm of new snow / Strong to extreme west winds / Freezing level at 1200mWednesday: Mix of sun and cloud with light flurries / Moderate southwest winds / Freezing level at 1100mThursday: Mix of sun and clouds / Moderate southwest winds / Freezing level at 1000m

Avalanche Summary

On Sunday, several size 1 wind slabs were ski cut in the Lizard Range. On Monday, new snowfall and strong winds are expected to have produced a solid round of wind slab activity at all elevation bands, although no formal updates from the field were available at the time of producing this bulletin . The new snow buries a weak interface which will likely prolong the reactivity of new slabs.

Snowpack Summary

By Monday afternoon, up to 45cm of low-density snow had fallen with the highest amounts accumulating in the Lizard Range. Intense wind transport was reported to have occurred at all elevations, and reactive wind slabs are expected to exist. The new snow buries a variable surface that developed over the last week of cold, dry, and windy conditions. This interface consists of scoured surfaces and wind slabs in wind exposed terrain, widespread faceting of the upper snowpack, and surface hoar up to 20 mm in sheltered areas. In sheltered areas, you may find another layer of surface hoar in the mid to upper snowpack which was buried around December 10. The mid pack is generally well settled. The thick crust from mid-November is near the bottom of the snowpack and reports suggest that the crust is currently well bonded to the surrounding snow.

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.