Avalanche Forecast

Archived

Apr 5th, 2017–Apr 6th, 2017

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches possible, human triggered probable.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches possible, human triggered probable.

Regions

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Dangerous avalanche conditions will persist in the Mt. Baker area Thursday so avoid consequential avalanche terrain. There's a lot of new snow above 5000 feet, maintaining the low probability/high consequence potential for very large avalanches above treeline and large wet snow avalanches below treeline.

Detailed Forecast

A stalled frontal boundary oriented north-south and to the west of the Cascades will finally lift to the northeast and out of the area Thursday morning. After a period of light to moderate rain and snow, post-frontal showers, heaviest in the Mt. Baker area will follow in the afternoon. More sunshine should mix in for the central-west and southwest Cascades in the afternoon.

New storm and wind slab problems will dominate in the NW zone including Mt. Baker, where there has been over 2 inches of water in the last day or so. With the snow-line oscillating around 5000 feet Wednesday night and Thursday, expect lingering storm slab and wind slab near and above treeline. New storm slab may be touchy especially if there is a daytime warning trend on Thursday. Realize that in the Mt. Baker area, initially shallow storm slabs may step down to deeper layers from earlier in the storm cycle.

New wind slab should exist above treeline and perhaps down into the near treeline elevation band. Avoid recently wind loaded slopes with fresh wind slab most likely on NW-SE aspects. Deep wind slab may exist above treeline particularly in the northwest zone.

Rainfall at lower elevations should activate loose wet avalanches on steeper slopes. Extended afternoon sunbreaks and daytime warming should increase the likelihood of loose wet avalanches on solar aspects in all elevation bands. Watch for wet surface snow deeper than a few inches, pinwheels and initial natural releases that indicate an increasing loose wet avalanche danger.

Other avalanche problems not listed in the problem set:

Potentially large and destructive wet slab avalanches are possible in isolated areas in the Mt Baker area near and below treeline on Thursday where recent rainfall has been the heaviest. Glide avalanches may also be possible in this area.

Recent cornices are very large and have likely been weakened during this most recent storm cycle. Natural cornice releases and resulting slab avalanches are dangerous and unpredictable. Give cornices a wide berth if traveling along ridge-lines and avoid slopes below large cornices. See a blog post regarding cornices here.

Snowpack Discussion

Weather and Snowpack

March was a wet and wild month for weather and avalanches in the Cascades. The last widespread avalanche cycle during this stretch occurred March 28th-29th.

A weak front crossed the Northwest on Saturday morning 4/1, causing light rain mainly along the Cascade west slopes. This was followed by an upper trough that caused some light amounts of snow along the Cascade west slopes at much cooler temperatures on Sunday.

Fair but cool weather has been seen in the Olympics and Cascades Monday and Tuesday. Reports generally indicate strong surface or near surface crust layers and shallow recent snow.

A stalled frontal boundary on Wednesday brought heavy rain and snow to the Mt. Baker area with much much lighter precipitation for the central-west and southwest Cascades. Snow levels were generally between 4500-5500 feet on Wednesday.

Recent Observations

North

NWAC pro-observer Lee Lazzara was at Little Devil Peak in North Cascades on Monday 4/3. Near and above treeline Lee found about 4 inches of recent storm snow over the most recent crust, and wind slabs averaging about 1 foot on N-E aspects below ridges. Snowpack tests indicated triggering of wind slabs to be stubborn. There was evidence of recent large cornice failures. The recent strong rain crust dominated the snowpack below treeline with shallow wet snow conditions during the afternoon. Shallow cold snow was preserved on steep shaded terrain near and above treeline.

Central

On Sunday 4/2, the Alpental pro-patrol only reported minor amounts of new snow on the crust from last week and no avalanches.

South

No recent observations.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). 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.

Wind Slabs

Wind Slab avalanches are the 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.

Loose Wet

Loose Wet avalanches are the 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. 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.