Avalanche Forecast
Regions: Mt Hood.
Mt. Hood will have significant storm related avalanche danger Friday. Avoid wind loaded slopes near and above treeline and steeper slopes at lower elevations Friday to stay safe.
Detailed Forecast
Skies may partially clear Friday or feature filtered sunshine in the afternoon as a frontal system lifts north into British Columbia. Freezing levels should rise to around 10,000 ft Friday and alpine winds should fall off during the day.  Unlike the Washington Cascades, Mt. Hood will have significant storm related avalanche danger Friday.Â
Winds slabs will be found near and above treeline Friday and should be sensitive to human triggering. Avoid wind loaded slopes and watch for obvious clues like snowpack cracking. As winds veer to northerly above treeline Thursday night, snow will be transported to SW aspects.Â
Storm slab instabilities should be quick to settle out on Friday, but look for the greatest sensitivity through mid-day or in areas where graupel layers accumulated during heavier showers Thursday afternoon and may act as a bed surface.Â
Small loose wet avalanches are possible on steeper slopes involving new snow storm especially near and below treeline. Watch for wet snow deeper than your boot tops, especially on steep solar slopes during the late morning to afternoon hours. Even if skies remain mostly cloudy, strong solar input in mid-April will affect the snow surface on solar slopes. Â
The potential for cornice releases should be low Friday but will increase through the weekend. Cornice releases can be unpredictable during the spring so avoid areas below cornices and remember that cornices can break much further back than expected along ridges.
Although not listed as an avalanche problem, large, powerful glide avalanches can release unexpectedly so avoid areas below steep unsupported slopes or rock faces showing glide cracks.
Snowpack Discussion
Weather and Snowpack
We've had two big warm-ups and spring shed cycles since the end of March. Over this time period the snowpack has undergone significant settlement with lower elevation snow beginning to fade away and with an overall transition to a spring snowpack.
On Tuesday afternoon and night a frontal system brought a few inches of snow to the Mt. Hood area. A low pressure system brought another round of snow Wednesday night and Thursday with 6-8 inches of new snow seen at the Timberline and Mt. Hood Meadow NWAC stations through Thursday afternoon. Winds were moderate out of the S or SW above treeline Thursday transporting new snow to lee slopes.Â
After a relatively cool week, the upper snowpack has generally drained and refrozen near and above treeline and on non-solar aspects. However it's quite variable how supportable the underlying crust is throughout the terrain. At lower elevations and on solar aspects, wet grains likely remain dominant in the upper snowpack. Â
Frequent March storms built unusually large cornices along many ridges. The potential for low probability/high consequence encounters, such as cornice failures and glide avalanches from steep unsupported slopes and smooth rock faces will continue through the spring.Â
The mid and lower snowpack along the west slopes should generally be a stable mix of crusts and layers of moist and rounded snow crystals.
Recent Observations
Mt. Hood Meadows pro-patrol reported small wind slabs building on lee N-NE aspects Thursday above treeline that were sensitive to ski cuts and easily showed cracking and propagation. In the deepest areas, the slabs were locally up to 2' by mid-day Thursday.Â
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: 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: All aspects.
Elevations: All elevations.
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: All elevations.
Likelihood: Possible
Expected Size: 1 - 1