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 Wind Slabs and Loose Wet.
NWAC,
Northwest Avalanche Center
Moderate E-SE winds in the Paradise, Crystal, and Snoqualmie areas may have built recent shallow wind slabs Tuesday and Wednesday in the near and above treeline zones. Look for signs of firmer wind transported snow that can indicate wind slab layers.
Newly formed wind slab is more likely in the Snoqualmie Pass area and south, near and above treeline, on a variety of aspects.
Summary
Detailed Forecast
Mild daytime temperatures and sunshine 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.
Moderate to strong east winds seen around New Years Eve through the weekend built wind slab on west aspects, primarily in the central and the south Cascades including the Cascade Passes. These wind slabs led to several avalanche incidents and likely the fatality on Granite Mountain near Snoqualmie Pass a week ago Thursday. Subsequent warmer weather and a week of time have likely allowed these layers to bond and strengthen and there have been no avalanches reported on these older wind slabs recently.
A pattern change Sunday, Jan. 3 led to moderating temperatures and a period of snowfall early this week, with about 6-12 inches falling along the west slopes. This new snowfall accumulated on the surface hoar and near surface faceted snow from around the New Year on many non-solar or sheltered slopes. A few reports, via the NWAC observation page, confirmed several small soft slab releases occurred or stability tests indicated, the storm snow failed on these recently buried weak layers. However, Pro-patrol reports in snowpack tests or during control work generally reported the new snow lacked cohesiveness and therefore lacked the slab character necessary to propagate or allow for a slab avalanche.
Warming temperatures Thursday are allowing for more bonding and strengthening of this layer and field observations Thursday in the Crystal Mtn backcountry indicated this layer gaining strength and failed to propagate during ECT tests. Surface crust layers were noted on solar aspects with some settled powder still providing good conditions on shaded slopes.
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: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
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
Valid until: Jan 8th, 2016 10:00AM
