Avalanche Forecast

Archived

Apr 26th, 2018–Apr 27th, 2018

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

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Warm temperatures and sun will create heightened avalanche conditions on Friday. You can trigger wet avalanches and cornices. Plan your travel to be out of avalanche terrain before afternoon.

Detailed Forecast

The avalanche danger will increase to Moderate by late Friday morning. Due to warm temperatures and strong sun, you can trigger wet avalanches. Plan your day to be out of avalanche terrain before the snow becomes wet and unsupportive.

You can trigger Loose Wet avalanches on slopes over 35 degrees. Use extra caution on large, steep, and unsupported slopes where you may be able to trigger a large avalanche. If you sink in wet snow up to the top of your boots, avoid slopes over 35 degrees. If warm temperatures and sun continue into the afternoon you may be able to trigger Wet Slab avalanches. Wet Slabs can be dangerously large and are difficult to predict. Limit your exposure to large start zones and overhead avalanche paths suspect for Wet Slab avalanches.

Give cornices a wide buffer. Cornices can break surprisingly far back from the edge. Make sure you are well off and out from under cornices, especially as the sun is shining on them. Cornice fall could be big enough to kill you and could trigger other avalanches.

Snowpack Discussion

A long stretch of warm weather and strong sun has ushered in spring-like avalanche concerns. An extensive cycle of Loose Wet avalanches and cornice falls occurred this week throughout the Cascades. As the warm temperatures have continued loose avalanches have been moving to higher elevations and more polar (northerly) aspects. Slab avalanche activity due to warming has been occurring, though not as widespread or showing major patterns.

Generally, Wet Slabs or slab avalanches entraining wet snow in the past week have occurred in the upper snowpack with a few deeper releases reported. In the Mt Baker area and North Cascades National Park west of the Cascade Crest observers have reported a significant cycle of slabs 3-6 feet (1-2 meters) deep. One observer reported probing a widespread weak layer 3 meters below the surface on the Silver Glacier.

On Thursday, Forecaster Dallas Glass reported a natural cornice fall as well as easily triggering Loose Wet avalanches near the Alpental Valley. Dallas reported that a thin surface crust quickly softened in the morning.

Problems

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.