Avalanche Forecast
Regions: Cascades - West.
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.
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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.
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Avalanche Problems
Wind Slabs
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.
Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..
Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.
Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.
Aspects: North, North East, East, South East.
Elevations: All elevations.
Likelihood: Likely
Expected Size: 1 - 1
Storm Slabs
Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. 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.
You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.
Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1