Avalanche Forecast
Regions: Mt Hood.
The snowpack in the Olympics and Cascades is undergoing a lot of change and there is less than the usual certainty in which avalanche problems and danger levels to indicate. It might be a good plan to wait until Friday when conditions are better known and should be more stable.
Detailed Forecast
Winds and snow showers will decrease Wednesday night and Thursday with cooler temperatures.
Lighter storm snow should be seen above about 6000 feet at Mt Hood by Thursday.
New wind slab may be possible at higher elevations on the volcanoes where storm snowfall is heaviest. Underlying crusts may make wind slab sensitive on some slopes.
New storm slab will be most likely in any areas that experience rapidly accumulating snow of more than an inch an hour for several hours. Underlying crusts may make storm slab sensitive as well on some slopes.
The snowpack in the Olympics and Cascades is undergoing a lot of change and there is less than the usual certainty in which avalanche problems and danger levels to indicate. It might be a good plan to wait until Friday when conditions are better known and should be more stable.
Snowpack Discussion
Weather and Snowpack
An Arctic air mass was over the Northwest with fair, cold weather last week. Surface hoar and near surface faceted crystals probably formed in most areas during that period.
A drastic change was seen when an atmospheric river moved to the Northwest Tuesday and Wednesday. This caused rain up to about 7000 feet at Mt Hood.
Observations the next couple days should help determine to what extent any of the surface hoar and near surface faceted crystals from the fair cold weather might have survived the atmospheric river event.
Recent Observations
A couple reports for Mt Hood area available via the NWAC Observations page for last Thursday. A skier on the north side of Mt Hood noted E and W wind effects and potential wind slab in the near and above treeline. Another skier on Pea Gravel Ridge noted limited, thin wind slab near the top of the Ridge but otherwise snow was right side up and cornice and ski tests gave no results.
NWAC pro-observer Laura Green was touring in the east fork of Hood River up to 6100 feet on Friday. She found the upper snowpack generally non-reactive in snowpack tests with good skiing conditions especially below treeline. Good surface hoar growth was noted up to 6100 feet.
The Mt Hood Meadows pro-patrol on Wednesday reports that rain penetrated about 10 inches into the snow with no results during explosive avalanche control. Visibility was low on Wednesday and it could not be determined if there had been any natural avalanches on the upper mountain.
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, South East, North West.
Elevations: Alpine.
Likelihood: Possible
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: All elevations.
Likelihood: Possible
Expected Size: 1 - 1