Avalanche Forecast
Issued: Apr 1st, 2015 11:20AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Loose Wet and Wind Slabs.
NWAC,
Northwest Avalanche Center
Sunshine and daytime warming may melt and weaken the recent storm snow, especially on solar aspects. Also, watch for weakening cornices and possible wind slabs near ridges.
Summary
Detailed Forecast
Partly cloudy skies with sunny periods, cool temperatures and light winds are expected Thursday.
In areas that have enough snow cover to provide a bed surface, shallow, loose wet avalanches involving the recent storm snow will be possible with daytime warming. Also, lee easterly aspects may harbor shallow wind slab at higher elevations.
Cornices won't be listed as an avalanche problem but be aware of new cornice growth along ridgelines.
Many areas at lower elevations and further away from the Cascade crest do not have enough snow to cause an avalanche danger.
Snowpack Discussion
During the fair and mild weather Monday, avalanche professionals working in the Washington Pass area triggered significant slides Monday using explosives. Wet slab avalanches entrained moist snow in the with Liberty Bell paths and buried the closed highway with several feet of debris. Little natural avalanche activity was observed in the area.
Snow levels fell quickly after a front moved through early Tuesday morning with scattered showers near the Cascade crest through Wednesday afternoon depositing an inch or two near and above treeline. In many areas, the old moist surface should be slowly re-freezing, with the new snow generally bonding well, keeping avalanche concerns confined to new storm snow layers.
Snowdepths vary greatly across the east slopes with a regionally healthy snowpack in the northeast Cascades to bare solar and lower elevation slopes in the central and southeast Cascades.
Problems
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.
Aspects: East, South East, South, South West, West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
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
Valid until: Apr 2nd, 2015 11:20AM
