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Archived

Avalanche Forecast

Jan 27th, 2016–Jan 28th, 2016
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
2: Moderate
The avalanche danger rating below treeline will be moderate
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
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Olympics.

In the Olympics the main problem should continue to be loose-wet avalanches on Thursday. Watch for wet surface snow deeper than a few inches and pinwheels or roller balls that usually precede loose wet avalanches.

Detailed Forecast

Periods of moderate to heavy rain overnight Wednesday and early Thursday will cause further wet snow conditions, including increasing the likelihood of loose-wet avalanches on steep slopes.

In the Olympics the main problem should continue to be loose wet avalanches Thursday. Watch for wet surface snow deeper than a few inches and pinwheels or roller balls that usually precede loose wet avalanches. This may be more likely on non solar slopes holding loose snow, but will be indicated on all aspects. 

Previous wind slab in the above treeline may be loaded and weakened by wet surface snow. This avalanche problem may be getting unlikely, but watch for signs of previous firmer transported snow mainly on northwest to southeast aspects.

Cooling and rain turning to snow showers is expected later Thursday. This should allow for a good bond to develop between the previously wet surface snow and new snow. Only light snow showers are expected later Thursday, with shallow new snow amounts expected. This should allow for a newly forming crust to begin stabilizing the snowpack. 

Snowpack Discussion

A warm front last Thursday caused heavy rain in the Olympics and this caused a loose wet avalanche cycle on steep slopes in all the elevation bands.

This was followed by cooler weather and shallow new snow. The cooling formed good bonding to the forming crust as observed by NWAC pro-observer Matt Schonwald Friday.

Matt reported generally stable surface snow conditions with no layers of concern in the BTL and NTL elevation zones. Overall the snowpack consisted of a few inches of saturated snow, well bonded to supportive dryer, old snow and a newly forming crust. Stability tests were all negative. Some transport of loose surface snow was seen being deposited on the northerly facing terrain below ridges, but no distinctive wind slab had formed as of Friday afternoon.

A strong front, moving into the Olympics Wednesday afternoon, is bringing increasing rain at high freezing levels. This is wetting and saturating surface snow layers, increasing wet snow conditions. 

 

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.

Aspects: All aspects.

Elevations: All elevations.

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, North West.

Elevations: Alpine.

Likelihood: Unlikely

Expected Size: 1 - 1