Avalanche Forecast
Issued: Feb 14th, 2016 10:00AM
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
The continued warm wet weather Monday will maintain wet snow conditions near and below treeline. New wind slabs and cornices should maintain dangerous avalanche conditions near and above treeline Monday.
Summary
Detailed Forecast
Light to moderate rain and snow is expected with strong winds and moderately high freezing levels Monday. The greater precipitation will shift from the southern zones Sunday night to the north WA Cascades Monday.
Some steep slopes may have released naturally by Monday due to warming and light rain, locally lowering the danger on those slopes, however on slopes that have not released, natural or triggered avalanches should remain possible Monday.
Wind slabs should build on lee slopes below ridges at the higher elevations, Mainly N-SE facing near and above treeline.
Watch for fresh cornices along ridges and stay well clear.
Loose-wet avalanches will be a concern on steeper slopes at lower elevations. Watch for wet snow that gets deeper than a few inches.
Snowpack Discussion
Weather and Snowpack
Two fair weather periods in January allowed surface hoar and near surface faceting to occur. These persistent weak layers were buried intact on Jan 3rd and 11th, but are no longer considered a persistent slab threat after several warm and wet systems tested this layer and it has been unreactive where it can still be identified in recent snowpit tests. A warm and wet system late last month caused a rain crust to form in most areas and elevations along the east slopes on Jan 28th.
The warmest weather of the winter occurred this past Sunday through Wednesday with extended temperatures climbing into the 50's in most areas east of the crest. The warm temperatures and solar effects earlier in the week caused loose wet avalanches and overall snowpack consolidation, leaving behind a crust as temperatures cooled Friday.
A pair of warm fronts Thursday night through Sunday morning deposited about 6-12 inches of storm snow over most east slope locations, with the greatest amounts in the NE zone.
Recent Observations
A professional observation from the northeast zone Saturday indicated that storm snow of about a foot remained cold and provided good ski conditions near and above treeline and was well bonded to the recent melt-freeze crust. Areas of wind slabs formed on some lee slopes below ridges due to moderate west wind transporting loose surface snow Friday night.
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.
Elevations: Alpine, Treeline.
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 15th, 2016 10:00AM
