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Archived

Avalanche Forecast

Mar 8th, 2014–Mar 10th, 2014
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
3: Considerable
The avalanche danger rating below treeline will be considerable
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Olympics.

A decreasing avalanche danger is expected on Sunday. Wet snow avalanches should still be the main concern Sunday.

Detailed Forecast

Another potential major wet loose avalanche cycle is likely during frontal passage and heavy rain or snow at warmer temperatures Saturday afternoon and night. Cornice failures are also likely during that period.

But rain or snow showers decrease rapidly on Sunday morning at slightly cooler temperatures. Significant new snow is not expected or should be very limited. A decreasing avalanche danger is expected on Sunday.

The main concern will be lingering wet loose snow avalanches. This is most likely on steep slopes that do not release on Saturday night. Watch for further pinwheeling of surface snow and wet snow still deeper than a few inches which often precede this type of avalanche. Loose wet avalanches may still entrain deeper wet snow and be large and destructive.

New small shallow of wind slab might be possible above treeline. The lack of new snow should limit this new concern. Watch for signs of firmer wind transported snow.

Small shallow new areas of storm slab might be also be possible above treeline. But again the lack of new snow and the cooling trend should greatly limit this concern.

Snowpack Discussion

Past

A two week storm cycle ended about 25 February that produced about 9 feet of generally wet heavy snowfall at Hurricane and avalanche cycles across the region.

Warm and mainly dry weather at the end of February led to wet snow avalanches and melt/freeze crusts throughout the region. 

The current storm cycle began last weekend with initially cool temperatures and poor bonds to the end of February crust in many areas. This storm cycle is turning out to be almost as wet as the last one! Water equivalents and snowfall for the current storm cycle will be about 5 inches but only about 2 feet of snowfall at Hurricane ending Sunday morning. This cycle has been producing many avalanches all week in the Cascades including reports from Holden Village, Stevens Pass, Tumwater Canyon, Alpental and Snoqualmie with pass closures at times last week.

Recent

A short break in the current storm cycle was seen on Friday causing some further consolidation and temporary stabilizing.

NWAC observers Tyler and Katie Reid on Friday reported wet and saturated upper snow pack layers with no positive snow pit test results but with numerous wet loose avalanches to size 2. Warming effects had penetrated quite deeply into upper snowpack layers.

Here is a video from Tyler and Katy at Hurricane on Friday.

A refreeze of wet snow surface on Friday night should have brought some temporary relative stability on Saturday morning.

The mid and base pack around Hurricane Ridge should still consist of stable crusts and melt form layers from periods of warm weather earlier this winter. Also in the below tree-line zone on solar aspects rain and mild temperatures may keep the shallow snowpack wet and unconsolidated. 

Avalanche 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.

Elevations: Treeline, Below Treeline.

Likelihood: Likely

Expected Size: 1 - 2

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 East, East, South East.

Elevations: Alpine.

Likelihood: Possible

Expected Size: 1 - 1

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: All aspects.

Elevations: Alpine.

Likelihood: Unlikely

Expected Size: 1 - 1