Avalanche Forecast

Issued: Mar 29th, 2015 11:00AM

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

Northwest Avalanche Center NWAC, Northwest Avalanche Center

Less recent snow and rain has given the snowpack east of the crest a chance to partly consolidate and mostly stabilize.

Summary

Detailed Forecast

Frontal moisture should mostly lift north to BC  Sunday night to Monday afternoon. Fair weather is expected east of the crest.

Past snow has had a chance to partly consolidate and mostly stabilize east of the crest. Possible loose wet avalanches should be the main problem and will be emphasized on solar slopes but watch for loose wet conditions on all aspects.

Older wind slab may linger on previous lee slopes. Watch for possible firmer previously wind transported snow mainly on north to east aspects.

Cornices won't be listed as an avalanche problem. But avoid slopes below cornices and ridges or summits where cornices may be hard to see in all areas.

Snowpack Discussion

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

The DOT crew working at Washington Pass early last week reported 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.

A warm front caused only light amounts of rain and snow east of the crest Wednesday to Thursday morning with gradual warming along the east slopes. NWAC Observer Tom Curtis was on Nason Ridge on Thursday and reported small to medium rollerballs and evidence of recent small to large loose wet avalanches.

A front and short wave crossed the Northwest Friday night causing strong west-southwest winds, some rain and snow and lowering snow levels. But rain and snow amounts were light east of the crest.

Frontal moisture is moving mainly to BC Sunday. But fair weather is generally being seen east of the crest.

Problems

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: South East, South, South West.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 1

Wind Slabs

An icon showing 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.

Likelihood

Possible

Expected Size

1 - 1

Valid until: Mar 30th, 2015 11:00AM