Avalanche Forecast
Issued: Mar 25th, 2015 11:00AM
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
Partly sunny skies in the north and mostly sunny skies in the south Thursday along with high freezing levels will maintain the threat of loose wet avalanches, especially on solar slopes near and above treeline that did not naturally avalanche Wednesday.
Summary
Detailed Forecast
Partly sunny skies in the north and mostly sunny skies in the south Thursday along with high freezing levels will maintain the threat of loose wet avalanches, especially on solar slopes near and above treeline that did not naturally avalanche Wednesday.
Avoid steeper slopes if you are sinking in more than a few inches, and be aware the even small loose wet avalanches are powerful and can push you into unintended terrain features. Isolated slides may become larger and more powerful by entraining light amounts of snowfall from earlier in the week.
Fresh cornices along ridgelines have likely been weakened and should become susceptible to failure Thursday with warming and potential sunshine. Make sure to give them a wide berth, and be aware of corniced slopes above you.
Lingering wind slab is possible above treeline on lee aspects especially above Wednesday's snow line.
Less recent snow and ample terrain anchors may limit the avalanche danger below treeline. Many areas at the lowest elevations do not have enough snow to cause an avalanche danger.
Snowpack Discussion
The 15-18 inches of snow that fell about March 14th-15th mainly in the northeast Cascades has settled or melted by at least 10 inches and probably been mostly absorbed into the upper snowpack. The storm last weekend only deposited light amounts of new snow to most of the east slopes.
The DOT crew working at Washington Pass on Monday and Tuesday reports mostly stable overall snow conditions with 4-6 inches of recent snow above the pass and about 2 inches at pass level. One natural loose dry avalanche was seen at about 6500 feet on Silver Star Peak on Tuesday.
Only light amounts of rain and snow fell Wednesday along with a gradual warming trend along the east slopes.
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, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Mar 26th, 2015 11:00AM
