Avalanche Forecast
Regions: Olympics.
Wet snow conditions will persist with Loose Wet avalanches now possible at all elevations. Avoid slopes with terrain traps where you see evidence of new rollerballs, pinwheels, and small Loose Wet avalanches. Recent rain and warm temperatures have weakened Cornices so give them a wide berth and be aware of overhead hazard. Older persistent weak layers may still exist in the upper snowpack around Hurricane Ridge. Use caution on open slopes greater than 35 degrees on N-E aspects near and above treeline.
Detailed Forecast
Relatively dry and warm conditions are expected Friday. Wet snow conditions will persist with Loose Wet avalanches now possible at all elevations. In isolated areas, Loose Wet avalanches may become large if they gouge down to deeper layers.  Avoid slopes with terrain traps where you see evidence of new rollerballs, pinwheels, and small Loose Wet avalanches.Â
Recent rain and warm temperature have weakened Cornices. Give Cornices a wide berth if traveling along ridgelines as they often break back further than expected. Be aware of overhead hazard if traveling on slopes with Cornices above as they may fail naturally or be human-triggered.Â
Older persistent weak layers may still exist in the upper snowpack around Hurricane Ridge. It can be difficult to assess and manage Persistent Slab avalanches. You can use snowpack tests to confirm the presence of these weak layers, however, they are not a decision making tool. You can avoid triggering a Persistent Slab avalanche by staying off of open slopes greater than 35 degrees on N-E aspects near and above treeline.
Recent shallow Wind Slabs formed earlier in the week may still exist in isolated areas above treeline (above ~6000 ft) on lee slopes. Use visual clues such as blowing snow, fresh cornices, and cracks in the snow all indicate you could trigger a Wind Slab avalanche.Â
Snowpack Discussion
Periods of light rain and a rising snowline allowed wet snow conditions to extend into the near and above treeline elevation bands Thursday. On Wednesday, shallow amounts of wet snow accumulated above about 5000 ft.Â
Three to six inches (8-15cm) of snow fell at Hurricane Ridge last Sunday through Monday morning. Light to moderate winds during the storm transported the new snow, likely forming new shallow and reactive wind slabs at higher elevations. This new snow fell on melt-freeze crusts in most locations.Â
Older weak snow has been observed on N-E aspects near and above treeline. Weak sugar facets may be found just above a melt-freeze crust. This layer is generally 1.5 to 2 feet (45-60cm) below the snow surface. Regular above freezing day-time temperatures over the past 10 days since the last reported avalanche at this interface have likely helped stabilize these older weak layers, but more information is needed to put Persistent Slab concerns to rest.Â
There are no other significant layers of concern in the snowpack at this time.
Observations
No avalanche activity has been reported in the Hurricane Ridge area over the last week.Â
Last Friday 3/30, NPS Rangers performed snowpack tests on a NNE aspect at 5,000 ft. They reported test results indicating propagation on a layer of weak old snow about 2 ft below the surface.
On Thursday, 3/29 NWAC professional observer Matt Schonwald saw evidence of two recent slab avalanches releasing on steep convexities on NE aspects between 5200-5400 ft. These avalanches released on a weak layer, poorly bonded to a hard crust. Several snowpack tests on this layer confirmed the propensity for avalanches to propagate.
Avalanche Problems
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.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 1
Persistent Slabs
Release of a cohesive layer of soft to hard snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slabs.
The best ways to manage the risk from Persistent Slabs is to make conservative terrain choices. They can be triggered by light loads and weeks after the last storm. The slabs often propagate in surprising and unpredictable ways. This makes this problem difficult to predict and manage and requires a wide safety buffer to handle the uncertainty.
This Persistent Slab was triggered remotely, failed on a layer of faceted snow in the middle of the snowpack, and crossed several terrain features.
Persistent slabs can be triggered by light loads and weeks after the last storm. You can trigger them remotely and they often propagate across and beyond terrain features that would otherwise confine wind and storm slabs. Give yourself a wide safety buffer to handle the uncertainty.
Aspects: North, North East, East.
Elevations: Alpine, Treeline.
Likelihood: Unlikely
Expected Size: 1 - 1