Avalanche Forecast
Regions: Stevens Pass.
The avalanche danger should mainly shift to new snow layers by the end of the daylight hours on Tuesday.
Detailed Forecast
A weakening cold front will cross the Northwest on Tuesday morning. This should cause light rain or snow with cooling temperatures.
Then a stronger short wave should cross the Northwest Tuesday afternoon and night. This should cause increasing rain or snow beginning in the Cascades Tuesday afternoon.
The rain mainly Tuesday afternoon should help small wet loose avalanches remain possible mainly near and below treeline on Tuesday. Watch for wet surface snow deeper than a few inches, pinwheeling of surface snow and small natural wet loose releases that usually precede more major wet loose snow avalanches.
New small wind slab should become likely starting Tuesday afternoon mainly above treeline on lee slopes. Watch for signs of cracking or firmer wind transported snow.
New small areas of storm slab should also become likely starting Tuesday afternoon also mainly above treeline on sheltered slopes. This is most likely in any areas that receive heavier snowfall.
In many areas the cooling trend may also bond new snow to old snow and build favorable stable new snow profiles.
Snowpack Discussion
We have shifted avalanche concerns to more recent storm layers and moved away from deeper snowpack concerns for the near term.
A wet cold front 15-17 March stalled over the Olympics and the north Cascades and then produced mainly rain before changing to snow in a north to south fashion across the area. NWAC sites near and west of the crest picked up 5-20 inches of snow. Some storm and wind slab avalanches were seen but instability was not widespread due to a cooling trend, good bonding to the old snow and short lived storm layers.
Another cold front crossed the Northwest Wednesday. Snowfall at NWAC sites near and west of the crest ranged from 3 to 19 inches by Thursday morning with a further cooling trend. Lesser amounts were seen south of Mt Rainier. The Alpental ski patrol reported a limited natural avalanche cycle Wednesday night. On Thursday a skier in a NNW facing chute at 5400 feet called Fluer di Lis at Stevens Pass triggered a 6-8" storm slab and lost gear but fortunately was uninjured. A backcountry report on the NWAC observation page from Ruby Mountain Friday indicated a favorable profile with a temporary storm layer in the recent snow and 1 small triggered soft slab on a steep convex roll near the summit. NWAC observer Jeff Ward was at Jim Hill near Stevens Pass on Friday - here is a video. NWAC observer Jeff Hambelton at Stevens Pass on Friday reported a natural storm slab that released due to daytime heating on a west aspect at 5600 feet.
Reports from Saturday indicated some powder surviving on north slopes and wet loose avalanches on solar slopes. NWAC obsever Dallas Glass and a report on Turns All Year from Crystal indicated small to large triggered wet loose snow avalanches. These wet loose conditions are expected to be continuing Sunday and this warm Monday on solar slopes.
Granite Mountain Accident Sunday afternoon: Around 4:45 PM on Saturday afternoon 2 skiers and a dog began descending the skier's right avalanche path on the south side of Granite Mountain. They triggered a slab avalanche that stepped down to a deeper slab. Upon review of crown photos and conversations with local avalanche professionals from Snoqualmie Pass it seems most likely that the initial slab failure on this cross loaded path included the Wednesday storm snow. The deeper second slab of similar depth included 16-17 March storm snow with the bonds between these layers weakened by strong solar input and potential melt water in the upper snowpack during the afternoon. The best estimate right now is that both slabs were at least 1 foot in depth.
The skier caught and killed in the avalanche skied off the ridge at about 5200 feet and onto a steep (40+ degrees) slope. The avalanche became a large and destructive funneling down to around 2300', entraining increasingly wet snow lower in the avalanche path and at times gouging to the ground. Size estimates are at least D3/R3. The other person was in a safe zone and not affected. The skier that was caught was buried under 20 feet of debris but was recovered Sunday morning by local search and rescue personnel. Another party of two on the lower mountain was not caught and aided in the preliminary search efforts.
Photo of Granite Mountain avalanche taken 23 March 2014 by Jason Skipper.
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: 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, Treeline.
Likelihood: Likely
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, Treeline.
Likelihood: Likely
Expected Size: 1 - 1