Avalanche Forecast

Archived

Jan 12th, 2018–Jan 13th, 2018

Alpine

Natural avalanches possible, human triggered probable.

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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Weather factors across the area will drive the loose wet avalanche problem Saturday. Watch for clues such as big changes in the weather, pinwheels, and roller balls to indicate wet surface snow conditions are developing. Heavy snowfall has accumulated across the area this week and that deserves respect. Wind slabs and storm slabs are gaining strength, but this takes time.

Detailed Forecast

Local weather will drive avalanche problem development Saturday. In the south warm temperatures and clearing skies will allow loose surface snow to develop on sunny slopes. In the north, light rain will continue to create moist surface snow conditions near and below treeline. In the central Cascades and passes, rain in the morning and clearing in the afternoon will cause moist surface snow conditions. Pay attention to the weather. Note changes in precipitation and sky conditions, and anticipate how this will affect potential loose wet avalanches.

Near and above treeline lingering wind slabs and storms slabs area expected. Mild weather will continue to allow these problems to gain strength, but this takes time.

The west slopes and passes have received a substantial amount of snow this week. Any avalanche may entrain significant new snow or step-down to deeper layers resulting in avalanches that area larger than anticipated.

Ease into terrain on Saturday. Significant precipitation, recent natural avalanche cycles, and limited observations all warrant stepping out with caution.

Snowpack Discussion

Light rain Friday fell across the west slopes of the Cascades. Rain reached elevations of 5500 feet in the south and 4800 feet in the north. Moist to wet surface snow below treeline resulted in a natural loose wet avalanche cycle Thursday night and Friday morning.

Above the rain line, a series of storms Wednesday through Friday has deposited 2 or more feet of cold snow. Multiple weaklayers were found within the storm snow. A widespread natural storm slab cycle from Thursday has been reported from the Stevens, Snoqualmie, and Crystal backcountry areas. Observations show these weaknesses gaining strength, but this takes time.

Winds redistributed snow throughout the storm, depositing snow onto a variety of aspects. Limited information about above treeline terrain has been received due to poor visibility and difficult travel conditions. A high degree of uncertainty exists in the above treeline areas.

The recent storm snow sits on a thin 1/9 crust found up into the near treeline elevation band in most areas. A more supportable and thicker 1/5 crust from rain or freezing rain is easily identifiable in the upper snowpack.

Below the 1/5 interface, observations continue to indicate a strong snowpack with no notable layers of concern.

Observations:

North

Mt Baker Ski Patrol reported rain to 4800 feet at the ski area Friday. Recent loose wet avalanche activity was observed below treeline in surrounding terrain. Low visibility limited observations into the near and above treeline terrain outside the ski area.

Central

Snoqualmie Pass DOT reported rain reaching up to 5400 feet in the Alpental area Friday. A loose wet avalanche cycle occurred Thursday night below treeline. Some loose wet avalanches ran for 1000 feet and entrained significant snow.

Thursday was a very touchy and active avalanche day at Stevens Pass and Snoqualmie Pass. NWAC forecaster Dallas Glass observed numerous natural storm slab avalanches on all aspects near and below treeline in around the immediate Stevens Pass backcountry. Storm slabs released within new storm layers, occasionally stepping down deeper to a storm layer from Wednesday 1/10. Pro-patrol reported natural storm slabs released in the Alpental Back Bowls Thursday. Storm slabs were very touchy during control work at Alpental throughout the day with paths reloading quickly during heavy snowfall.

South

NWAC professional observer Jeremy Allyn traveled in the Crystal Mountain backcountry Friday. He observed rain to 5400 feet. In near treeline areas observations showed storm snow weaknesses gaining strength. Evidence from Thursday's natural storm slab cycle was evident on all aspects in the surrounding terrain.

Problems

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.

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.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.