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Avalanche Forecast

Archived

Dec 23rd, 2014–Dec 24th, 2014

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

Regions

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The main avalanche problems Wednesday should be new wind slab and new storm slab.

Detailed Forecast

Northwest winds, decreasing snow showers and much lower snow levels will be seen on Wednesday. About 6-12 inches of new snow seems likely mainly in the near and above treeline near and west of the crest by Wednesday morning.

The main avalanche problems Wednesday should be new wind slab and new storm slab. These new layers should be found mainly in the near and above treeline. Avoid travel on steep lee slopes with firmer wind transported snow that is a sign of wind slab. Storm slab should be limited to steep slopes in areas that receive more than an inch of snow an hour for at least several hours.

A persistent weak layer will not be indicated near and west of the crest for the early December crust layer unless it shows signs of activity in the future.

Have a plan in place before you get to the trailhead. Confidence is fair for this forecast.

 

Snowpack Discussion

A strong warm storm moved over the Northwest Saturday and Sunday. Triggered storm slab avalanches were seen such as at Silver Basin near Crystal Mountain.

Collapsing and whoomping was also seen over the weekend near and west of the crest including Mt Baker and Silver Basin near Crystal Mountain. This was apparently due to an early December crust at 60-110 cm below the surface.

See the NWAC Recent Observations for information from the weekend including a good snowpit video from 20 December from Oyvind Henningsen.

Decreasing winds, a little cooling and snow was seen at the tail end of the storm Sunday night. A relative break and some stabilizing was generally seen Monday.

A moist cold front is moving over the Northwest Tuesday to Wednesday morning. This will be accompanied by strong southwest winds, moderate to heavy rain changing to snow, and lowering snow levels.

 

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.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.