Avalanche Forecast
Regions: Cascades - North West.
A MODERATE danger means human triggered avalanches are possible. Watch mainly for possible wind slab on a variety of aspects and for possible loose wet avalanches on steep solar slopes. Watch out for dangerous tree bombs and stay in sight of your partner.
Detailed Forecast
Sunny weather should be seen on Thursday. Warmer temperatures should be seen at higher elevations in the north Cascades by Thursday afternoon. Cool temperatures with possible low clouds should be seen in the Cascade passes especially Snoqualmie.
This weather should allow older wind slab to continue to slowly settle and stabilize. Wind slab will most likely be found on north to southeast aspects near and above tree line. New wind slab may also be found on west to northwest aspects mainly in the Cascade Passes. Any wind slab avalanches should be confined to surface layers. Watch and test for inverted strong over weak storm snow.
The sunny weather and warmer temperatures at higher elevations mainly in the north Cascades should bring the possibility of loose wet avalanches Thursday 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.
A lot 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 on Thursday afternoon. A tree bomb can be just as fatal as an avalanche!
There have been snow immersion fatalities in tree wells already 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. A weak weather system Sunday and Monday helped create some new mostly small and mostly shallow wind slab in many areas.
There have been numerous triggered wind slabs the past week but with each passing day the ease of trigger seems to be diminishing. Storm slabs have all but settled and are no longer a problem of note. Storm snow has been gradually settling but remains mostly right side up and continues to offer some excellent conditions.
Here are summaries for a couple of the latest reports for the west slopes.
A report via the NWAC Observations for Moonlight Bowl on Skyline Ridge at Stevens Pass on Tuesday indicated generally unreactive wind slab and right side up snow on steep north slopes and no signs of instability.
NWAC pro observer Lee Lazzara was in the Bagley Lake area near Mt Baker on Tuesday 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 Mountain.
NWAC pro observers Dallas Glass and Ian Nicholson were on Chair Peak at Snoqualmie today 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.
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.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 1