Avalanche Forecast
Issued: Jan 7th, 2016 10:00AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Loose Wet and Wind Slabs.
NWAC,
Northwest Avalanche Center
Watch for melting and weakening of surface snow on solar aspects. Avoid steep slopes at higher elevations suspected of wind deposited snow. Wind slab avalanches should become less sensitive, but remain possible to trigger on specific terrain features.
Summary
Detailed Forecast
Mild daytime temperatures and some sun breaks, mainly at higher elevations, should allow for shallow surface snow melt, breaking down existing surface crusts through the day, where they existed. Cooler settled powder is likely on steeper shaded slopes.
Small loose wet avalanches should be less likely Friday, but will still be possible on direct, steep, solar aspects.
Also, watch for any recently formed cornices as the sun and warming may weaken these, especially near midday.
Watch for recent wind slabs on a variety of aspects, mainly near or above treeline and avoid slopes where even being caught in a small slide could have larger consequences, such as slopes above trees, cliffs or where the terrain would funnel snow into a trap, like a creek bed or natural depression.
Snowpack Discussion
About a week of fair weather was centered around the New Year. This allowed the significant snow that fell during a strong storm cycle, that ended about Christmas, to settle and stabilize. It also led to extensive surface hoar and near surface faceted snow to develop on non-solar, sheltered slopes. These weak surface snow conditions were from seen in numerous reports both west and east of the WA Cascade crest. On solar aspects, a thin sun or melt-freeze crust formed during the stretch of high pressure.
Since Sunday, a few inches of steady light snow have accumulated along the east slopes, with up to 12 inches at Mission Ridge with only moderate SW ridge-top winds.
Tom Curtis was west of Blewett Pass around Iron Mountain, New Years Day and found the December 13 buried surface hoar layer 60 cm down that showed sudden collapses in several column tests, including PST with a firm slab overhead. In this area, the layer was prevalent on NE-E aspects around 5300 ft near treeline. This may be a layer of concern to track or look for moving forward in this specific area.
PST End down 60cm on 20151213 buried surface hoar layer. West of Blewett Pass, January 1, 2016. ENE aspect NTL @ 5330ft. Photo: T. Curtis
The North Cascades Mountain Guides on January 1st and 2nd at Washington Pass generally report good stable conditions and a lack of results in snow pit tests. Minor wind effects have been noted near ridges.
Reports via the NWAC observations page for January 2nd at Blewett Pass, email received at the NWAC from Holden for January 3rd and further reports via the NWAC observations page for January 4th for Stevens and Snoqualmie, and most recently Tuesday the 5th on Red Mountain near Salmon La Sac help confirm the extent of the recently buried surface hoar.
Thanks for this observation posted Tuesday which includes a nice video example! http://www.nwac.us/observations/pk/277/
Avalanche professionals in the Tumwater Canyon area Wednesday reported the 1/3 surface hoar layer about 20 cm down on a NW aspect at 4000 ft, but lacking the cohesiveness to present a slab problem. The surface hoar layer was also found on solar aspects at this elevation.
Several loose-wet slides were also reported Thursday afternoon depositing wet snow in the Tumwater Canyon area due to warming temperatures.
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
Expected Size
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, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Jan 8th, 2016 10:00AM
