Avalanche Forecast
Regions: Olympics.
A very strong storm is expected Thursday. Heavy precipitation with a warming trend will cause a rapidly increasing avalanche danger with dangerous avalanche conditions developing through the day Thursday. Conservative decision-making will be essential. Avoid steep open slopes and watch for changing conditions.
Detailed Forecast
 A very strong storm arrives in the early morning hours Thursday, reaching peak intensity in the middle of the day. Heavy snowfall and very strong winds with a warming trend will build unstable snow layers in most steep terrain.Â
The new heavy storm snow will load existing shallow 4-8 inches of low density snow that has fallen over the past few days. Strong crust layers below will act as smooth sliding surfaces to allow avalanches to run long distances.Â
Expect whiteout and dangerous avalanche conditions Thursday. Best to travel in terrain well away from avalanche paths or slopes connected to steep open slopes above.
Snowpack Discussion
There have been about 4-6" of recent snow since Sunday. The underlying snow is very strong and has formed a supportable crust following last weeks warm temperatures to high elevations. The shallow, weak surface snow should not support the expected heavy snowfall by Thursday.
A strong crust layer below the shallow recent snow may act as a good bed surface for future avalanches. Â
The greatest potential for increased avalanche activity will be in areas that have a deeper consistent snowcover.
The height of snow across the terrain is quite variable. Many areas have little to no snowcover, even in higher terrain, where wind, rain and warm temperatures have stripped much of the season's snowfall. Numerous obstacles still exist at all elevations.
Observations
NPS rangers reported about 3 inches of new snow as of Tuesday morning. Â
NPS rangers Sunday morning reported snowfall on the drive up to Hurricane Ridge had begun to mix with ice pellets by 8 am Sunday morning. Temperatures stayed below freezing at Hurricane Ridge on Sunday with continuous light precipitation and gusty south winds.Â
Avalanche Problems
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: All elevations.
Likelihood: Likely
Expected Size: 1 - 1
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: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 1