Avalanche Forecast
Regions: Snoqualmie Pass.
Watch for possible loose wet avalanches and new small wind slab where there is significant new snow.
Detailed Forecast
A sharper shortwave will move north to south over the Northwest on Saturday. This will change flow from northwest to northeast and should cause light showers east of the crest Saturday with snow levels getting a little lower especially in the south Cascades.
The sun is getting stronger so small shallow loose wet avalanches also seem possible on Saturday on steep solar slopes where there is significant new snow west of the crest. This will be forecast from Stevens to the southwest zone but should be most likely from about Crystal to Mt Rainier where there will be the most new snow.
Where there is significant new snow west of the crest it also seems possible that northeast winds may build new small shallow wind slab on lee slopes. This should be mainly on unusual northwest to south aspects near ridges above treeline. But watch for this on other aspects as well due to the shifting and unusual winds. This will be forecast from Stevens to the southwest zone but should be most likely from about Crystal to Mt Rainier where there will be the most new snow.
Due to the low snowpack, especially below treeline, watch for terrain hazards such as open creeks, partially covered rocks and vegetation.
Snowpack Discussion
A benign weather pattern with mild temperatures was seen in the Olympics and Cascades for about 10 days through Wednesday. This caused thick surface crusts and more consolidation of the snow pack west of the crest.
A weak short wave moved over a temporarily flattened upper ridge on Thursday causing showers west of the crest. Northwest flow and possible weak convergence helped maintain showers west of the crest on Friday. From NWAC weather station data and reports it looks like by Saturday there will be anywhere from about 3-7 inches of new snow near and above treeline from about Stevens Pass to Mt Rainier with the most from Crystal to Mt Rainier.
Pro-observer Dallas Glass was at Paradise on Wednesday and reported some shallow softening on solar slopes, MF clusters throughout the snowpack and no instability. He was also at Paradise on Thursday and reported about 2 inches of initial new snow bonding well to previous snow and no avalanche problems.
The mid and lower snowpack west of the crest snow consists of layers of stable consolidated rounded grains or melt forms and crusts from multiple warm periods this winter.
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: South East, South, South West.
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: South, South West, West, North West.
Elevations: Alpine.
Likelihood: Possible
Expected Size: 1 - 1