Avalanche Forecast
Issued: Feb 17th, 2017 10:41AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Loose Wet.
NWAC,
Northwest Avalanche Center
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.
Summary
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
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.
Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..
Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.
Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine.
Likelihood
Expected Size
Loose Wet
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. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. 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.
Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.
Several loose wet avalanches, and lots of pinwheels and roller balls.
Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.
Elevations: Below Treeline.
Likelihood
Expected Size
Valid until: Feb 18th, 2017 10:41AM
