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Avalanche Forecast

Archived

Mar 14th, 2018–Mar 15th, 2018

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

Regions

Mt Hood.

Avalanche conditions are improving as the snowpack consolidates. Recent Wind Slabs will be more stubborn to trigger Thursday, but avoid any steep start zones suspected of receiving wind deposited snow. Give fresh Cornices a wide margin of safety. Watch for shallow wet snow conditions developing on steep southerly facing slopes during extended sun breaks.

Detailed Forecast

Cool weather Thursday with a mix of sun and light snow showers with light winds will allow for a gradual decrease in avalanche danger. Fresh shallow wind slabs near and above treeline will continue to strengthen and be more stubborn to trigger by Thursday. Still use caution and avoid steep lee slopes and cross loaded features that have received recent wind re-distributed snow.

Shallow recent snow may lead to small wet snow avalanches on steep sun exposed slopes during any extended sun breaks. Watch for rollerballs or pinwheels and snow falling from trees as signs of increasing wet snow conditions.

Lingering hard wind slabs may still exist at higher elevations. You are most likely to find and trigger these avalanches on shaded slopes not receiving direct sunshine. Firm wind slabs can lure you far onto the slope before failing, creating a particularly dangerous situation. To avoid wind slabs, stay away from any steep slopes where you believe winds have recently deposited snow. If the snow below you feels hollow, seek lower angle terrain.

Give recent cornices a wide margin of safety.

Snowpack Discussion

Sunshine and temperatures in the 40's to lower 50's the first few days of the week changed to a cool showery regime Tuesday. About 3-6 inches of new snow fell in showers by Wednesday in the Mt Hood areas. The overall snowpack has been gaining strength with strengthening melt-freeze crusts near the surface and only shallow recent snow above.

A period of moderate winds during the showers Tuesday and Wednesday has formed some shallow wind slabs on lee slopes in higher terrain. These shallow wind slabs should become more stubborn to trigger Thursday. 

Several melt-freeze cycles Saturday through Monday of this week continues to consolidate and strengthen the snowpack. 

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

Observations

Mt. Hood Meadows pro-patrol reported shallow wind slabs less than 1 ft  triggered by explosives on N-NE aspects near and above treeline Wednesday. On sun exposed slopes below treeline, a few rollerballs were showing signs of developing wet snow conditions.

Mt. Hood Meadows pro-patrol reported warmth and wet snow conditions on Sunday and again Monday, with generally small loose wet avalanches on steep sunny slopes. 

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.