Avalanche Forecast
Regions: Mt Hood.
Significantly changing weather and snow conditions should be seen at Mt Hood on Wednesday. Travel in avalanche terrain above treeline is not recommended. Dangerous conditions should also be seen in the near and below treeline.
Detailed Forecast
A weakening front should move over the Northwest Tuesday afternoon and night. This may cause some mostly light amounts of snow at Mt Hood but probably not as much as earlier expected.
The bigger story is the incoming atmospheric river on Wednesday. A warm front should south to north over the Olympics and Cascades Wednesday morning to afternoon. This should bring stormy wet weather with rising snow levels to Mt Hood starting Wednesday morning.
Mainly in the above treeline new wind slab of increasing density due to warming is very likely to form on lee slopes. Watch for firmer wind transported snow as the storm develops.
Also mainly in the above treeline new storm slab of increasing density is also very likely due to warming. Watch for snowfall that begins to accumulate at more than an inch an hour.
Rain in the below and possibly in the near tree line is also likely to create loose wet avalanche conditions. Watch for pinwheels and natural loose wet avalanches.
The rain where  heavy enough may activate previous layers and cause releases of previous wind slab layers or wet slab avalanches mainly in the near and below treeline.
Snowpack Discussion
Weather and Snowpack
Last week was wet and relatively mild with a series of active fronts transiting the region resulting in fluctuating freezing levels and periods of very strong winds (100+ mph gusts were not uncommon at the Mt Hood Meadows Cascade Express station).
The latter half of last week and the weekend featured more rain than snow at NWAC sites on Mt. Hood. For perspective, the averaged freezing level measured in March thus far has been 6600 feet at Salem; more akin to spring than late winter.Â
A front Sunday and a cooler upper trough Monday brought some snow with 2 day storm totals of about 8-9 inches at Mt Hood ending Tuesday morning.
The mid and lower snow pack at Mt Hood should be a stable mix of crusts and layers of moist and rounded snow crystals.
Recent Observations
On Saturday the Mt. Hood Meadows pro-patrol reported wet snow up to about 6600 feet with a thin crust above and a well consolidated snowpack in their area. Following the cool down Saturday night, pockets of shallow new wind slab were seen above treeline by Sunday morning.Â
On Monday there was about 5 inches of new snow and the Mt Hood Meadows pro-patrol reported a variety of conditions including isolated hard 12-18 inch wind slab on ENE slopes above treeline, wide spread sensitive 4-8 inch storm slab near treeline and small ski triggered loose wet avalanches below treeline on solar slopes.
The Mt Hood Meadows pro-patrol found that new and recent storm snow layers were less sensitive on Tuesday and that cooling had stabilized previous loose wet snow. Direct back country observations were not made on Tuesday but areas of 4-6 inch wind slab were still expected there.
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.
Elevations: Alpine, Treeline.
Likelihood: Very 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: Very 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.
Elevations: Treeline, Below Treeline.
Likelihood: Likely
Expected Size: 1 - 1