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Archived

Avalanche Forecast

Feb 6th, 2015–Feb 7th, 2015
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low

Regions: Mt Hood.

Expect increasing avalanche danger with elevation on Saturday... with new storm and wind slab avalanches possible near and above treeline. 

Detailed Forecast

Lowering snow levels and light to moderate precipitation late Friday night and Saturday should build new storm and wind slab above about 6000 feet. The avalanche danger should increase with elevation Saturday. 

The below treeline snowpack should be well drained and capable of handling additional rain without a significant increase in avalanche danger. Small wet loose avalanches will still be possible on steeper slopes below treeline. 

Remember, due to the unseasonably low snowpack especially at lower elevations, numerous terrain hazards such as open creeks, partially covered rocks and vegetation are widespread.  

Snowpack Discussion

Mild weather with sunny days or minor rain or snow was seen from about January 26th to about January 31st. This caused more consolidation, stabilizing and the formation of a thick strong stable surface crust in most areas west of the crest including Mt Hood.

Slightly wet weather from about February 1st through 4th produced about 5 inches of snow at NWAC sites at Mt Hood mixed with periods of rain. Frontal systems Thursday and Friday pushed snow levels up to around 7000-8000 feet with light rainfall accumulations at NWAC sites. 

Mid-week the Meadows patrol reported sensitive ski triggered 2-6 inch storm slab avalanches. On Wednesday, NWAC observer CJ Svela reported some natural loose wet avalanches and cornice drops on east aspects in the White River Canyon above treeline.

On Friday, the Meadows pro-patrol reported that the most recent snow was wet but well bonded and not causing any significant loose wet problems near and below treeline. 

The mid and lower snowpack at Mt Hood should consist of layers of stable consolidated rounded grains or melt forms and crusts from multiple warm periods this winter.

Avalanche Problems

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, Treeline.

Likelihood: Possible

Expected Size: 1 - 1

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

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: Below Treeline.

Likelihood: Unlikely

Expected Size: 1 - 1