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Avalanche Forecast

Archived

Apr 26th, 2018–Apr 27th, 2018

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 unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Snoqualmie Pass.

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

Detailed Forecast

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

You can easily trigger Loose Wet avalanches on most 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. Wet Slabs can be dangerously large and are difficult to predict. These avalanches may be difficult for a single person to trigger, but could occur naturally with cornice fall. Wet snow resting on a weak layer or crust is a sign that you can expect Wet Slab conditions. Limit your exposure to large start zones and overhead avalanche paths suspect for Wet Slab avalanches.

Give cornices a wide buffer. They will break naturally and you could easily trigger them. Cornices will often 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.

Wet Slabs

Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.