Avalanche Forecast

Archived

Feb 17th, 2017–Feb 18th, 2017

Alpine

Natural avalanches unlikely.

Treeline

Natural avalanches unlikely.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely.

Below Treeline

Natural avalanches unlikely.

Regions

Snoqualmie Pass.

A decreasing avalanche danger is expected Saturday as isolated wind slabs stabilize at higher elevations, while wet snow drains and continues to refreeze at lower elevations. There is an increased hazard from an uncontrolled fall on steep slopes with a smooth surface crust.

Detailed Forecast

Cloudy conditions with mostly light snow showers are expected through the day Saturday. Winds should remain light Saturday with only light snowfall accumulations up to a few inches.

This should allow for a gradual decreasing danger Saturday. Any isolated wind slabs formed late Thursday should continue to settle and stabilize at upper elevations. At lower elevations, wet or saturated snow should continue to drain and refreeze.

Continue to watch for any recent wind slabs that may have formed Thursday night, mainly easterly facing terrain near ridges above treeline.

Snowpack Discussion

Weather and Snowpack

Yet another atmospheric river arrived Tuesday night, bringing heavy rain to all forecast elevations in the west slopes of the Cascades zones. The storm total rain amounts ranged mostly from 1.5 - 4.5 inches of water, with the Mt Baker area receiving nearly 7 inches of rain by Thursday morning.

Localized freezing rain occurred during this event along the lower slopes of the Cascade Passes, where a variable strength, freezing rain crust formed at mid and lower elevations.

A slow cooling trend began overnight Wednesday with light to moderate snow showers depositing 2-6 inches of new snow by Thursday evening at mid and upper elevations.

A firm rain crust had set up by Friday in most areas with some areas at lower elevations maintaining a wet upper snowpack. The wet snowpack continues to drain and refreeze as of Friday.

Recent Observations

North

Thursday 2/16, the Mt Baker pro patrol reported a very large naturally triggered slab at the east end of Shuksan Arm that released sometime during the rain event. The initial estimates of the crown height are 20 feet!

Central

Alpental pro-patrol did not perform avalanche control Wednesday, but reported a 1/2" freezing rain crust up to about mid-mountain with rain falling on the upper mountain.

South

Dallas Glass was observing conditions at Paradise Thursday, 2/16. Dallas reported wet snow conditions in the upper two feet of the snowpack. Though previous rain events were allowing the liquid water to quickly drain, helping the stabilization process.

Problems

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.