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Avalanche Forecast

Archived

Jan 7th, 2016–Jan 8th, 2016

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

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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.  

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

Wind Slab avalanches are the 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.

Loose Wet

Loose Wet avalanches are the 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. 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.