Avalanche Forecast
Regions: Olympics.
Expect increasing avalanche danger on Wednesday as a front moves over the area. Watch for loose wet concerns in the morning and shallow but sensitive wind and storm slab in the afternoon.
Detailed Forecast
A quick moving but powerful frontal system should blow through the Olympics in the late morning to mid-day on Wednesday, with a strong cooling trend in the afternoon during post frontal showers.Â
Rain at lower elevations should allow for wet-loose concerns in the AM. Â While there is a favorable temperature trend with this storm watch for new storm instabilities during times of intense precipitation and expect fresh wind loading on lee slopes near and above treeline.Â
Take note on how the new storm snow bonds to the previous snow surface and watch for cracking on lower angled terrain as a sign of new storm snow instabilities.Â
Snowpack Discussion
A stalled and moist frontal boundary draped over mainly the north WA Cascades Saturday afternoon finally sagged south on Sunday, with rain changing to snow generally in a north to south fashion across the PNW mountains. A favorable temperature trend occurred with this storm, with gradual cooling from Saturday night through Sunday night.  From Saturday night through Monday morning Hurricane Ridge telemetry and NPS reports indicate about 18 inches of snow fell. Generally light showers at cool snow levels were seen through the day Monday, but moderate NW winds aloft likely transported snow Sunday night and continued into Monday in the alpine.Â
Over the weekend NWAC observer Katy Reid reported a generally well consolidated lower snowpack near treeline with moist snow from last week's periods of rain and warm temperatures reaching down from the upper to mid snowpack.  A NPS park ranger at Hurricane Ridge reported a backcountry skier on Sunrise Ridge above the road Sunday afternoon was able to ski cut and release a storm slab about 15-20 ft wide that covered the uphill lane with debris. Fortunately the skier was not caught in the slide due to daytime warming creating unstable slab conditions.
Gradual warming on Tuesday and a break between significant precipitation has likely allowed the most recent storm and wind slabs to settle and the snowpack should be relatively ready for the next incoming frontal system on Wednesday.Â
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: Possible
Expected Size: 1 - 1
Loose Wet
Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.
Several loose wet avalanches, and lots of pinwheels and roller balls.
Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.
Elevations: Below Treeline.
Likelihood: Possible
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: All elevations.
Likelihood: Possible
Expected Size: 1 - 1