Avalanche Forecast
Regions: Stevens Pass.
Heightened avalanche danger should be specific to wind-loaded slopes near and above treeline where recent east winds continue to build new wind slab. Loose wet avalanches are possible on steeper solar slopes, predominately away from the Cascade Passes and especially in the north Cascades.
Detailed Forecast
Ring in the New Year with sunshine, (except near the Cascade Passes where a mix of sun of clouds is likely)! Above freezing temperatures should work further east into the Cascades on Friday, with widely varying freezing levels seen across elevation bands and especially near the Cascade passes.Â
New wind slab will be the primary avalanche problem as moderate easterly winds continue to build new wind slab, including but not limited to westerly aspects. Older wind slab may still linger on more traditional N-SE aspects. Look for recently transported snow onto a variety of aspects and further downslope from ridgelines than you might expect. New wind slab is expected to be less of an issue in the north Cascades.
The sunny weather and warmer temperatures at higher elevations, especially in the north Cascades should bring the possibility of loose wet avalanches Friday afternoon on steep solar slopes. Watch for surface wet snow deeper than a few inches, initial roller balls and natural loose wet avalanches on steep solar slopes where snow may shed from rocks or cliffs.
Non-avalanche hazards: Copious amounts of snow has been seen in trees lately along the west slopes. Stay away from trees if you see trees starting to shed snow due to sunny weather Friday. A large tree bomb can be just as fatal as an avalanche! Also, there have been snow immersion fatalities in tree wells earlier this season at Snoqualmie and in Canada. Tree wells may still be lurking so stick near your partner in the trees and maintain visual contact. Â
Snowpack Discussion
A cool very snowy storm cycle brought 5-9 feet of snowfall along the west slopes the week ending December 24th. Light additional accumulations in the past week have allowed the snowpack to slowly settle with good skiing and riding conditions reported. A generally right-side up snowpack exists in non-wind affected terrain and widespread surface hoar and near surface faceting has been reported in sheltered areas in all elevation bands during the recent high pressure. The upper snowpack has generally stabilized, outside of surface sluffing and pockets of lingering wind slab over the past week.  Â
A few recent snowpack observations:Â
Tue: NWAC pro observer Lee Lazzara was in the Bagley Lake area near Mt Baker and found a generally right side up snow pack with some wind slab but also lacking a weak layer or interface. Lots of skiers around Bagley Lakes triggered only small loose dry avalanches. A small loose wet was also seen on the south side of Table Mt.
Wed: NWAC pro observers Dallas Glass and Ian Nicholson were on Chair Peak at Snoqualmie and reported that wind slab was a bit more prevalent there than the past couple days. Dallas triggered a small wind slab on a 35-40 degree north slope at about 5500 feet.They saw another skier triggered wind slab on a southwest slope about 600 feet below a ridge. They felt wind slab should be possible there on a variety of slopes and to 1000 feet below ridges.
Thu:Â Moderate east transport winds were observed from Snoqualmie down to Mt. Hood. Â NPS rangers from Mt. Rainier reported a small skier triggered wind slab on a west aspect near treeline Thursday morning. The slab was small, but east winds where continuing to load west aspects during the day.Â
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, Treeline.
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.
Aspects: South East, South, South West.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 1