Avalanche Forecast
Regions: Olympics.
Avalanche conditions are improving as the snowpack consolidates. Watch for fresh but shallow new Wind Slabs near ridges at higher elevations. Older weak snow may still exist in the snowpack so avoid large open slopes that may still harbor this difficult to predict and manage avalanche problem. Give fresh Cornices a wide margin of safety. Watch for shallow wet snow conditions on steep southerly facing slopes during extended sun breaks.
Detailed Forecast
Cool weather Thursday with a mix of sun and light snow showers with light winds will allow for a gradual decrease in avalanche danger. Fresh shallow wind slabs near and above treeline will continue to strengthen and be more stubborn to trigger by Thursday. Still use caution and avoid steep lee slopes and cross loaded features that have received recent wind re-distributed snow.
The late winter sun is becoming strongly effective at producing wet snow avalanches. Watch for extended sun breaks on steep southerly facing slopes quickly wetting and weakening surface snow. Watch for rollerballs or pinwheels and snow falling from trees as signs of wet snow conditions.
Recent warm weather and snowpack settlement has helped round and strengthen buried persistent weak layers. We have removed the Persistent Slab problem from the forecast problem list, however this does not mean it is impossible to trigger a persistent slab in isolated areas, especially with a larger trigger such as a cornice fall.Â
Avoid large open slopes, especially slopes below large overhanging cornices.Â
Snowpack Discussion
Sunshine and temperatures in the 40's to lower 50's the first few days of the week changed to a cool showery regime Tuesday. Only a few inches of new snow fell in showers by Wednesday. The overall snowpack has been gaining strength with strengthening melt-freeze crusts near the surface and only shallow recent snow above.
A period of moderate winds during the showers Tuesday may have formed some shallow wind slabs on lee slopes in higher terrain. Any shallow wind slabs should become more stubborn to trigger.Â
Several melt-freeze cycles Saturday through Monday of this week continues to consolidate and strengthen the snowpack.Â
Older weak snow layers were reported in the Olympics last week. On slopes that receive direct sun, several facet/crust layers may be found. A more widespread layer of weak sugary facets was found just above a very firm melt-freeze (2/8) crust formed in early February, but continues to gain strength. The depth to this weak layer depends on aspect and elevation.
We have not received reports of recent avalanches in the Olympics other than small wet loose on steep sunny slopes.
There are no significant layers of concern below the 2/8 crust layer.
Observations
On Sunday as of 1 PM, NPS rangers reported generally small loose wet avalanches with one larger release caused by a partial cornice collapse.Â
On Saturday, Forecaster Robert Hahn and NPS Rangers found the 2/8 weak snow/crust interface in snowpits on a West aspect at 5300' and down 2.5 feet from the surface. No new avalanche activity was observed other than small wet loose avalanches on steep sunny slopes. North facing terrain still held drier settled powder.Â
On Wednesday March 7th, a NPS ranger traveled in the Victor Pass area and found many crusts with facets forming on south aspects. Near ridge-tops, the 2/13 weak layer was 8-12" down and 3 mm facets were observed. Mid-slope this layer was down 3-4 feet.
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, West, North West.
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: Treeline, Below Treeline.
Likelihood: Possible
Expected Size: 1 - 1