Avalanche Forecast

Issued: Mar 27th, 2015 11:00AM

The alpine rating is moderate, the treeline rating is moderate, and the below treeline rating is low. Known problems include Storm Slabs and Loose Wet.

Northwest Avalanche Center NWAC, Northwest Avalanche Center

Use caution in higher elevations where possibly greater new snow may accumulate, especially lee slopes near ridges. Watch for areas of wet snow at mid elevations, and during daytime warming. 

Summary

Detailed Forecast

 

A frontal passage Friday night should cause some light new snow, but initially rain changing to snow should leave good bonding of new snow to the old wet snow surface. 

Watch for areas where new snow has been transported by wind to lee slopes at higher elevations along ridges. Also, watch for cornice development that may be soft and sensitive to trigger or release from daytime warming.

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 1-2 feet of snow that fell in mid-march, mainly in the northeast Cascades, has settled or melted and likely been absorbed into the upper snowpack. 

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. 

Sunshine and very warm temperatures Thursday and again Friday have likely created significant surface snow melt, leading to consolidated melt-freeze conditions. 

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

Storm Slabs

An icon showing Storm Slabs

Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. Storm-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.

 

You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.

 

Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.

Aspects: North, North East, East, South East, North West.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 1

Loose Wet

An icon showing 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

Possible

Expected Size

1 - 1

Valid until: Mar 28th, 2015 11:00AM