Avalanche Forecast
Issued: Mar 17th, 2018 11:12AM
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
You may find isolated wind slabs on lee slopes at higher elevations where shallow fresh wind slabs may be able to trigger. Avoid steep slopes above treeline where you think recent wind loading has occurred. Sun breaks and daytime warming will help soften the surface snow making shallow Loose-Wet avalanches possible, especially in the Timberline area with greater new snow. Watch for new roller balls or wet surface snow deeper than your ankle, and avoid travel on those steep slopes.
Summary
Detailed Forecast
Use caution around steep wind loaded slopes at higher elevations Sunday where you could trigger a wind slab. Use visual clues such as blowing snow, fresh cornices, and snow drifts to identify and avoid wind loaded slopes. You will be most likely to trigger a wind slab on steep convex roll overs, unsupported slopes, or on cross-loaded features.
In other locations, generally safe avalanche conditions exist. Cloudy skies, cool temperatures, and light showers will limit the avalanche hazard in the Mt Hood area. Watch for signs of unstable snow, especially sunshine affecting fresh snow, especially in the Timberline area where greater fresh snow has fallen since Saturday. If you encounter rollerballing or natural Loose-Wet avalanches, avoid travel on those steep sun exposed slopes.
Snowpack Discussion
As of Saturday afternoon, snow showers have been widely variable in the Mt Hood area with the Timberline area receiving about 8 inches of new snow and only 1-2 inches in the Mt Hood Meadows area. The new snow has fallen with cool temperatures and some occasional moderate westerly winds near ridgecrest.
Above treeline, shallow and isolated wind slabs have formed early last week. The most recent snow sits atop a melt-freeze crust.
Several melt-freeze cycles last weekend helped to consolidate and strengthen the snowpack. No recent avalanche activity has been reported at Mt. Hood.
While we are tracking several layers deeper in the snowpack, there are currently no significant layers of concern.
Observations
On Friday, Pro-observer Laura Green found 2-4" of new snow near Timberline well bonded to the underlying crust. Poor visibility limited observations above treeline.
On Wednesday, Mt. Hood Meadows Pro-Patrol reported shallow wind slabs less than 1 ft deep triggered by explosives on N-NE aspects 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: All aspects.
Elevations: Alpine.
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.
Aspects: East, South East, South, South West, West.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Mar 18th, 2018 11:12AM
