Avalanche Forecast

Archived

Mar 9th, 2018–Mar 10th, 2018

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

Mt Hood.

New and reactive wind slabs have formed on lee slopes in the Mt Hood area. Use visual clues such as snow drifts, snow pillows, and fresh cornices to identify and avoid slopes where the wind has deposited snow. Sunshine Saturday will create wet surface snow conditions. Stay off of steep sunny slopes where you see new rollerballs and pinwheels. Limit your exposure to Mt Hood’s very large avalanche paths. Large avalanches may start high on the mountain and travel down valley to your location.

Detailed Forecast

You will be able to trigger wind slab avalanches on lee slopes and cross-loaded features Saturday. Visual clues such as snow drifts, cracking, and fresh cornices can help you locate and avoid steep slopes where winds have deposited snow. Some of these wind slabs may be very firm and break above you. Give wind loaded terrain a wide berth.

Very large wind slabs may have formed above our forecast area on Mt Hood. If one of these avalanches starts, it may travel down to lower elevations. Limit your exposure to Mt Hood’s very large avalanche paths.

A strong March sun will quickly warm up sunny slopes creating wet surface snow. This will happen first on steep rock slopes receiving direct sunshine. Expect new roller balls, pinwheels, and small loose wet avalanches to occur. Stay off of any steep slope where you see signs of wet surface snow conditions.

Snowpack Discussion

Six to eight inches of new snow fell with moderate winds Thursday night and Friday. Winds throughout the storm reshaped the snow surface. Firm wind slabs, snow drifts, and wind scoured surfaces have all been reported.

In sheltered areas generally loose snow surfaces exist.

While we are tracking several layers deeper in the snowpack, there are currently no significant layers of concern.

Observations:

NWAC Pro-Observer Laura Green traveled in the Mt Hood backcountry Friday. Laura found moderate to strong winds transporting snow throughout the day. Plumes were seen high on Mt Hood during the morning. She observed a variety of wind featured snow surfaces including large deep snow drifts, hard wind slabs, and uneven snow surfaces near and above treeline.

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.