Avalanche Forecast
Regions: Olympics.
You can trigger slab avalanches Saturday on north and east aspects at upper elevations. Watch out for steep roll-overs (convexities), unsupported features, and larger terrain of consequence. Warmer temperatures and sun are making it easier to trigger wet avalanches on steep, rocky, and sun exposed slopes. If you see recent roller balls, Loose Wet avalanches, or experience wet surface snow deeper than your ankle, move to shaded and drier slopes.
Detailed Forecast
You can trigger Persistent Slabs on shaded slopes at mid to upper elevations. Persistent Slabs are difficult to manage and can break in surprising ways. To stay safe, avoid where the problem exists or if you go there stick to lower angle slopes and limit your exposure to large avalanche paths.
Warm temperatures and sun on Saturday will make it easier to trigger wet avalanches, especially in areas where they haven't recently run. Loose Wet avalanches may occur at higher elevations or on more shaded aspects (facing west, north, and east). While Loose Wet avalanches are often smaller and easier to predict, they can be dangerous in high consequence terrain. Avoid extreme terrain or areas where getting caught in a wet avalanche would be especially dangerous. This includes steep slopes above rocks and cliffs, tight gullies, or trees.
Minimal freeze Friday night raises concern for other warming and wet snow related avalanches. Watch out for snow-covered rock slabs at mid to lower elevations and slopes with exposed cracks where Glide avalanches could occur. Cornices have built in the past week. They typically fall during warming periods like what we will experience on Saturday. Whether you're walking on a ridge or traveling on slopes, give cornices plenty of room. Wet Slabs are very difficult to predict and can be very large and destructive. Avoid avalanche terrain, if you find slopes with unsupportive, wet snow or where a known weak layer is getting wet.
Snowpack Discussion
Temperatures have warmed over the last several days with mild daytime temperatures. Only shallow recent snowfall of 1-2 inches have accumulated, mostly Thursday with little to no snow earlier this week.  This has allowed for snowpack settlement and the development of a strengthening melt freeze crust. Older Wind Slabs have now stabilized.Â
There has been recent slab avalanches, likely released over the past few days on a weak layer above a strong melt-freeze crust buried about 1.5 ft on lee slopes above Hurricane Ridge. This layer has been tracked over the past few weeks but has now produced at least two slab avalanches, each with crown depths about 1.5 ft and propagating over 100 ft wide on NE aspects between 5200-5400 ft.Â
There are no other significant layers of concern in the snowpack at this time.
Observations
On Friday, NPS Rangers performed snowpack tests on a NNE aspect at 5,000ft. They reported test results indicating propagation on a layer of weak old snow about 2 feet 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
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: 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.
Aspects: East, South East, South, South West, West.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 1