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Archived

Avalanche Forecast

Jan 17th, 2016–Jan 18th, 2016
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
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

Regions: Mt Hood.

Even with an overall stabilizing trend on Monday, dangerous avalanche conditions will exist on lee wind-loaded slopes and where storm slabs remain sensitive to human triggering. Take it slow on Monday and evaluate the snowpack as you travel conservatively through the terrain.  

Detailed Forecast

Showers should taper off Monday morning and a few sunbreaks are possible mid-day before cloud cover increases Monday afternoon ahead of the next frontal system. 

Wind slab should be found mainly on lee north to east slopes near and especially above treeline. Very large avalanches are possible on lee slopes if initial releases are able to step down to a crust formed earlier this month. Generally avoid wind loaded slopes above treeline.  

Storm slabs may become more cohesive and likely to trigger with day-time warming and some sunshine. Choose lower angled slopes if you find sensitive storm layers.  

Small loose wet avalanches should be likely on steeper slopes below treeline involving small amounts of recent storm snow. Watch for loose wet avalanches near terrain traps, where even a small avalanche could have unintended consequences. 

Snowpack Discussion

The latest period of active weather from January 12-17th has accumulated about 3 feet of snow at both the Mt. Hood Meadows and Timberline Mt Hood NWAC stations. Fluctuating snow levels over this period has occasionally mixed rain up into the near treeline elevation band during this storm cycle.

A very active day on avalanche control was seen at Mt Hood Meadows Friday. The pro patrol reported explosively triggered widespread 1-4 foot slab avalanches on north to east slopes above treeline releasing on a crust from last weekend along with very sensitive ski cutting as well. 

On Saturday, rain moved up to at least 6000 feet by late morning with snow levels lowering by mid-afternoon. Visibility was limited, but Meadows pro-patrol found 8-12" wet slabs very sensitive to ski cuts on steeper slopes below treeline. Steady winds continued to load lee aspects near and above treeline Saturday. Another 0.50 - 1 inch of water on Sunday brought up to 6 inches of wet snow at Meadows and Timberline through 5 PM. 

Avalanche Problems

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, Treeline.

Likelihood: Likely

Expected Size: 1 - 2

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: All elevations.

Likelihood: Likely

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: Likely

Expected Size: 1 - 1