Avalanche Forecast
Regions: Cascades - North West.
Careful snowpack evaluation and conservative decision-making are essential near and above treeline. Rain and warm temperatures have created dangerous avalanche conditions. Wet, heavy snow and wind have built recent slabs above treeline. You can trigger wet avalanches near and below treeline. If you see Wet Slab avalanches, avoid avalanche terrain.
Detailed Forecast
Snow, wind, rain, and warm temperatures have combined to create dangerous avalanche conditions. Wind has drifted slabs on lee slopes above treeline. In some locations, these new slabs will overly lower density snow from earlier in the week. Visual clues such as blowing snow, fresh cornices, and cracks in the snow all indicate that you could trigger a Wind Slab avalanche. Observations have been limited from upper elevation and forecasters are less certain about conditions at these elevations.
Careful snowpack evaluation and conservative decision-making are essential near and above treeline. Over the past week, observers have reported especially reactive avalanches on both last weekends storm interface (4/1) and surface hoar that was buried on 3/25 (2 feet below the surface). Recently triggered avalanches have been due to new snow and wind, but have broken in surprising ways. Use snowpack tests to help you identify if these layers are still present in the snowpack. On many slopes they may have gotten wet or rounded.
Rain has set the stage for wet avalanche conditions. You may be able to trigger Loose Wet avalanches more easily near and above treeline than at lower elevations. However, the lower slopes are more rain-soaked. If water reaches buried crusts or softer layers of snow, Wet Slab avalanches could occur. Digging snow profiles can help you see the depth and extent of wet snow. That said, snowpack tests can be hard to interpret and Wet Slabs are hard to predict. They also can be very destructive. If you see slab avalanche activity in areas of wet snowpack, avoid traveling in avalanche terrain. There's a chance that large Glide avalanches could release naturally. Use extra caution and avoid stopping near and below snow covered rock slabs where Glide avalanches could occur.
Snowpack Discussion
Expect a lull in rain on Friday with warming temperatures. The wind stacked fresh slabs on older drifted slabs above treeline. Rain has moved into higher elevations and soaked previously dry snow laid down early this week. The April 1st-2nd storm deposited a relatively even blanket of 1.5 feet of snow across the Cascades West and Passes zones. In most locations, this new snow fell on a firm melt-freeze crust up to 5,500ft.
Observers have been tracking persistent weak layers deeper in the snowpack. The exact distribution of all of these layers is not well known. Where they have been found, there is good evidence that they are generally difficult to trigger.Â
Mt Baker: Several avalanches last Friday and Saturday failed on one of these layers of buried surface hoar (3/25). You are most likely to find this layer as a thin grey line 2-3 feet (60-90cm) below the snow surface on shaded slopes above 5000 feet. Additionally, a crust at the 4/1 interface has resulted in dramatic remote and skier triggered avalanches.
Crystal: A weak interface buried on 3/22 can be found 2-3 feet (60-90cm) below the snow surface. On sunny aspects, a thin layer of weak sugary facets can be found just above a firm melt-freeze crust. On shaded slopes buried surface hoar has been reported.
Below the top 2-3 feet (60-90cm), the snowpack is generally well bonded and significant layers of concern. The much older 2/8 melt-freeze layer can still be found over 6 feet (200cm) deep in the snowpack. While this layer isn't listed in our current avalanche problem set, it may reawaken if enough liquid water reaches it during the coming rain storms.
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Observations
North
On Wednesday, observers reported a skier triggered avalanche on a steep northeast aspect at 5,300ft in the adjacent backcountry. The skier was partially buried, but not injured.Â
On Monday Mt Baker Ski Patrol reported 12 inches (30cm) of new snow moderately well bonded to the old snow surface. Loose snow conditions were observed.
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: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Likely
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: All aspects.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 1