Avalanche Forecast
Regions: Mt Hood.
Possible overnight stormy conditions Monday night at Mt Hood make avalanche problems more likely on Tuesday than in the Washington Cascades.
Detailed Forecast
Light snow showers should decrease at Mt Hood Tuesday with fairly low snow levels.
Beware that the possible overnight stormy conditions may bring more snow and increase the likelihood of the avalanche problems at Mt Hood on Tuesday.
New likely wind slab should be expected on lee slopes mainly ATL or NTL at Mt Hood on Tuesday. Use extra caution near slope convexities where storm or wind slab avalanches are more likely to be triggered.
New likely storm slab should also be found in areas that receive more than an inch of snow an hour for more than several hours Monday night where there is less wind.
We are past the equinox and the sun is rapidly getting stronger and new snow will be susceptible to sun effects. Watch for likely wet snow deeper than a few inches or snowballing or natural loose wet avalanches by Tuesday midday on solar slopes. This is also more likely at Mt Hood if there is the expected heavier snowfall Monday night.
Remember the NWAC forecast applies to elevations up to the Cascade crest. A greater danger is often found above the crest on the upper volcanoes.
Less recent snow and ample terrain anchors should limit the avalanche danger below treeline. Many areas below treeline do not have enough snow to cause an avalanche danger at Mt Hood.
Snowpack Discussion
About 4-6 inches of snow was seen above about 6000 feet Saturday as reported by the Meadows ski patrol. The winds and new snow did build some stiff wind slab on northeast slopes up to 1 foot in places. But these stiff slabs were unreactive to ski cutting as the new snow fell on old wet snow and formed a good bond and thus were resistant to triggers.
No additional avalanche activity was reported Sunday by Meadows patrol.
A weak upper short wave and unstable air mass is moving over the Northwest on Monday. This is favoring the volcanoes including Mt Hood for snow showers. The Meadows patrol on Monday reported winds and rapid loading ATL. Ski cuts were beginning to cause 4-6 inch wind slab avalanches.
Another rapidly moving shortwave will carry a surface low across the north Oregon Cascades Monday night. This should bring possible overnight stormy conditions at Mt Hood.
The mid and lower snowpack at Mt Hood consists of layers of stable consolidated rounded grains or melt forms and crusts from multiple warm periods this winter. The snowpack at low elevations remains meager to non-existent.
Avalanche 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, North West.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 1
Storm Slabs
Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. 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.
You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.
Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 1
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: South East, South, South West.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 1