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East Slopes North - Canadian Border to Lake Chelan

Issued: 9:08 PM PST Saturday, March 3, 2018
by Robert Hahn

You can trigger Persistent Slab avalanches that could break widely over terrain features. These avalanches are difficult to predict and the consequence are life-threatening. Put a wide buffer of terrain between where you travel and open slopes over 35 degrees as well as large avalanche paths. Reduce your risk of triggering a Wind Slab avalanche by avoiding fresh wind drifts and cross-loaded features on steep slopes at upper elevations. 

Danger Scalei
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  • Low (1)
  • Moderate (2)
  • Considerable (3)
  • High (4)
  • Extreme (5)

Avalanche Problems for Sunday

Persistent Slabi

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Wind Slabi

  • Avalanche Problemi
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Forecast for Sunday:

An avalanche in the North Fork of the Teanaway resulted in 2 fatalities on Saturday. An NWAC forecaster visited the location of the avalanche and more details will be made available as soon as we have them.

The snowpack on the Cascades East slopes remains complex and dangerous.

It's currently much easier to trigger dangerous Persistent Slab avalanches on the East side of the Cascades compared to the West Slopes and there are multiple weak layers to avoid. Several layers of persistent grain types that have been reactive in tests are likely to remain reactive on Sunday. Several older weak layers of facets exist in the snowpack, but are still shallow enough that you can trigger them. In many areas with a deeper snowpack, you may get little warning signs of a Persistent Slab avalanche. While these avalanches are difficult to trigger, they are also very difficult to predict. A resulting avalanche will likely be large enough kill you. Put a wide margin of terrain between you and any slopes 35 degrees and steeper where you suspect the Persistent Slab problem. Continue to be cautious and stay away from steep, open slopes connected to large avalanche paths. If you experience collapsing or audible whumphs, avoid any nearby avalanche terrain. Snow profiles and snowpack tests can help confirm the presence of a weak layer but cannot prove its absence.

You are most likely to trigger Wind Slab avalanches above treeline on Sunday. You can avoid these avalanches by staying off of recent snow drifts, deeply pillowed features, and fresh cornices on slopes 35 degrees and steeper. These areas may exist far below ridge-lines and on mid-slope cross-loaded features. In some location soft non-wind-effected snow may cover new wind slabs making them harder to identify.

Avalanche Summary:

Up to a foot of snow has fallen with variable snow totals around the East Slopes since Wednesday with up to 2' of snow during the past week. Significant accumulations were reported as far east as Mission Ridge with the moderate to strong southerly flow during the storm on Wednesday and Wednesday night. This fresh snow has fallen on a variety of snow surfaces including thin sun crust, uneven wind surfaces, and soft unconsolidated snow. 

A number of potential persistent weak layers exist in the snowpack along the East Slopes of the Cascades. Two common layers that have been reported in many locations are a facet/crust combination buried on 2/23 and a facet/crust layer buried on 2/13. The exact layer and depth depend on aspect, elevation, and proximity to the Cascade crest. A high level of uncertainty remains surrounding these layers.

The upper (shallower 2/23) layer can be found 1-2 feet below the snow surface on steeper slopes that have received direct sun. Small weak facets have been found in other regions surrounding a thin sun crust formed early last week and buried during last weekend’s storms.

The deeper (2/13) facet/crust combination is typically found 2-3 feet below the snow surface. This layer has been around for two weeks with two confirmed skier triggered avalanches and more recent collapsing and whumphing. With significant new snow added to the snowpack last weekend, this layer may be reactive in areas where we have not seen previous avalanche activity nor snowpack test results. These weak sugary facets are located above a firm wide spread crust buried on Feb 5th.

The persistent slab in the North Cascades is likely reactive, but quite isolated. Wind slabs were becoming less reactive by Saturday.

While several layers exist in the snowpack, there are no significant layers of concern below the 2/5 crust.

Observations

North

On Saturday, NCMG traveled in the Cuthroat area and observed small wind slab avalanches in steep terrain that had run naturally on Friday. The 2/23 crust was not observed on north facing terrain above 5600'. The 2/13 layer down 3' (85 cm) at 6100' on a NNW aspect showed mixed results in tests with reactivity in deep tap tests, but not compression. Widespread collapses and a stubborn small persistent slab release was reported on Vasiliki ridge from a third party. 

On Friday, observers in the Washington Pass area reported continued test results indicating the potential for triggering Persistent Slab avalanches on the 2/13 facets.

Central

On Friday, NWAC observers Matt Primomo and Matt Schonwald traveled in the Bean Creek area north of Cle Elum. On both south and northeast slopes, they reported large and small column tests indicating potential for human triggering on the 2/13 facets. This weak layer was 3-4 feet below the surface. They also found the 2/23 facets about 2 feet below the surface on a south aspect at 5450 ft and several reactive layers of preserved snow crystals within the upper 1.5' of the snowpack.

On Wednesday, An avalanche professional in the Chiwakum Mountains reported collapses and whumps on the 2/13 buried facet layer. Depth to the layer was highly variable (1-3 feet). Another observer triggered an avalanche almost 3 feet deep on a small steep slope near McCue Ridge. 

No Corresponding Mountain Weather Forecast Available