Avalanche Forecast
Regions: Mt Hood.
A mix of increasing winter and spring avalanche conditions should be seen in the above treeline zone especially in the Washington Cascades near and west of the crest and at Mt Hood on Thursday.
Detailed Forecast
The cold front will cross the Northwest on Thursday with southwest winds and snow levels continuing at about 5-6000 feet during the day then lowering Thursday afternoon and night. This should produce about 5-10 inches of further new snowfall in the above treeline zone in the Washington Cascades near and west of the crest and at Mt Hood.
New or further building wind slab is likely on lee slopes mainly in that area. This should be north to southeast slopes or on cross loaded aspects or due to varied terrain may be seen on other aspects. Watch for signs of firmer wind transported snow or cracking snow.
New or further building storm slab is also likely on sheltered slopes mainly in the same area. This should be in areas that receive at least several inches of snowfall. Variations in winds and temperatures promote weak temporary storm layers that help cause storm slab.
The sun continues to get stronger as we get further into spring. Even with all the clouds on Thursday the sun could do its work mainly on solar slopes in areas where there is more than a few inches of snowfall. So wet loose avalanches are possible on such slopes. This will also be mainly in the above treeline zone in the Washington Cascades near and west of the crest and at Mt Hood but may extend down into the near treeline zone as well. Watch for increasing pinwheels and natural or triggered wet loose avalanches that increase in size or extent during the daylight hours.
Rain or much less new snow should continue in the near and below treeline areas on Thursday especially east of the crest. Less change in snow and avalanche conditions should be seen in those areas.
Note that the NWAC will issue a complete mountain weather forecast during the day and a complete avalanche forecast at 6 pm on Friday and Saturday.
Snowpack Discussion
A warm front is crossing the Northwest today with west-southwest winds and snow levels at about 5-6000 feet. This should produce about 4-8 inches of new snow in the above treeline zone in the Washington Cascades near and west of the crest.
So new wind slab on lee slopes and new storm slab on sheltered slopes should be starting to build in that area today.
Rain or much less new snow is expected in other areas today such as Hurricane, near and below treeline in the Washington Cascades near and west of the crest, east of the crest and at Mt Hood.
Avalanche Problems
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.
Likelihood: Likely
Expected Size: 1 - 1
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.
Elevations: Alpine.
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: East, South East, South, South West, West.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1