Avalanche Forecast
Regions: Cascades - North West.
The northwest Cascades should begin to see new storm and wind slab layers forming Tuesday afternoon.
Detailed Forecast
Some light showers should move to the Cascade west slopes on Tuesday morning. Increasing winds and light to moderate rain or snow should also reach the northwest Cascades Tuesday afternoon.
Watch for wind slab from the previous storm that will be most likely to linger on north to southeast slopes in the above treeline band Tuesday morning.
New wind and storm slab is likely to begin to form in the northwest Cascades starting Tuesday afternoon.
Snowpack Discussion
A strong warm storm moved over the Northwest Saturday and Sunday. Winds were seen to over 100 mph at some locations. Precipitation was generally heavy or very heavy near and west of the crest and moderate to heavy east of the crest. Precipitation fell as snow mainly in the above treeline zone Saturday and Sunday.
Easy tests, triggered storm slab avalanches, collapsing and whoomping were seen near and west of the crest including Mt Baker and Silver Basin near Crystal Mountain on Saturday as the storm was revving up. This action was seen at the early December crust at 60-110 cm below the surface.
No avalanches were reported Sunday due to stabilizing and a lack of back country travel.
Decreasing winds and a little cooling were seen at the tail end of the storm Sunday night and Monday with a little snow making it down to NWAC weather stations in the below treeline zones. No avalanches have been reported so far Monday and conditions will have greatly stabilized.
Some lingering wind slab and storm slab are likely mainly in the above treeline zone on Monday. A persistent weak layer will not be indicated for the early December crust layer unless it shows signs of activity in the future.
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: Alpine, Treeline.
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.
Likelihood: Possible
Expected Size: 1 - 1