Avalanche Forecast
Issued: Mar 14th, 2018 11:00AM
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
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.
Summary
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
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: North, North East, East, South East, North West.
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.
Elevations: Treeline, Below Treeline.
Likelihood
Expected Size
Valid until: Mar 15th, 2018 11:00AM
