Avalanche Forecast
Regions: Mt Hood.
Warmth and the late March sun will begin to shift the primary avalanche hazard to wet snow concerns Wednesday at Mt. Hood. High freezing levels, light winds and sunny skies over the next several days will increase the hazard, causing natural loose wet avalanches on solar aspects and increasing the odds for low likelihood/high consequence problems such as cornice failures. The loose wet potential will be greatest on steeper slopes below treeline.
Detailed Forecast
On Wednesday, persistent E-NE winds near and above treeline will slowly ease during the day and freezing levels should rise to around 10000 feet. Warmth and the late March sun will begin to shift the avalanche hazard to wet snow concerns Wednesday on Mt. Hood. High freezing levels, light winds and sunny skies over the next several days will increase the hazard, causing natural loose wet avalanches on solar aspects and increasing the odds for low likelihood/high consequence problems such as cornice failures.
Due to the firm wind packed surfaces near and above treeline and continuing moderate E-NE winds in the morning, wet snow avalanches will be less likely than in the Washington Cascades.
The loose wet potential will be greatest on steeper slopes below treeline. Melt-freeze crusts can quickly break down with intense spring sunshine. In areas that have received more recent snowfall, small loose wet avalanches have the potential to entrain deeper layers. Be aware of terrain traps where even a small loose wet avalanche could have unintended consequences. Plan to avoid steep solar slopes by late morning/mid-day to minimize the problem.  Â
A mix of older wind slab on lee easterly aspects and newer wind slab on south through westerly aspects will make wind slab avalanches possible on a variety of aspects, primarily near and above treeline. Watch for cracking and firmer or chalky wind transported snow.  Â
Many areas have large cornices along ridge-lines so be cognizant of the hazard above. Unlike the loose wet problem, you may not have much notice that a cornice is about to fail. Cornices can break much further back on ridges than expected and releases can be unpredictable during the spring.
Snowpack Discussion
Weather and Snowpack
Snow accumulations Wednesday 3/23 to Friday 3/25 varied based on elevation, with only a few inches below 5000 feet and about 8-10 inches at the Mt. Hood Meadows and Timberline stations. This snow was generally well-bonded to a moist crust buried March 22nd.
A strong front crossed the Northwest Sunday morning followed by a large upper trough and a cool unstable air mass Sunday afternoon and evening. Mt. Hood stations accumulated 10-12" of new snow through Sunday evening.Â
Skies were mostly sunny along the lower slopes Tuesday, but a warming trend was more muted at Mt. Hood due to cool and persistent NE winds.Â
Frequent March storms have built large cornices along ridges in many areas.
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
NWAC pro-observer Laura Green was out in Newton Canyon on Friday and found that winds had plastered the latest snow down with conviction, with moderate compression tests in the new snow and hard compression tests at the 3/22 interface. Limited rollerballs were seen on solar slopes. A size 2 natural avalanche from a potential cornice release was seen in White River Canyon.
Mt. Hood Meadows reported limited avalanche control results on Monday. NW winds Sunday night had transported snow to unusual aspects and into the below treeline band, but the new snow was generally bonded well in area. Another large natural avalanche was observed in White River Canyon above 8000 ft, likely releasing Sunday night.  A nice example of a reactive wind slab on a small slope was found in the Timberline area Monday. A 10" wind slab of denser snow released with a ski cut during warming Monday (photo below).Â
On Tuesday, NE winds transported snow above treeline again to non-traditional aspects. Unlike areas further north, the warming trend on Mt. Hood was muted Tuesday and the snow surface remained firm near and above treeline with a mix of hard wind slab, sastrugi and wind scoured surfaces. Meadows pro-patrol noted their below treeline terrain softening on solar aspects with increasing loose wet potential in the afternoon.  Â
Photo 3-28-16 by Alex Laudon, Timberline 6200 ft SE aspect
Avalanche Problems
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: All elevations.
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: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind lips of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
Cornices can never be trusted and avoiding them is necessary for safe backcountry travel. Stay well back from ridgeline areas with cornices. They often overhang the ridge edge can be triggered remotely. Avoid areas underneath cornices. Even small Cornice Fall can trigger a larger avalanche and large Cornice Fall can easily crush a human. Periods of significant temperature warm-up are times to be particularly aware.
A corniced ridgeline. A large cornice has formed at the top of the ridge. A smaller cornice has formed to the left of the trees from crossloading.
Cornices are easy to identify and are confined to lee and cross-loaded ridges, sub-ridges, and sharp convexities. They are easiest to trigger during periods of rapid growth (new snow and wind), rapid warming, and during rain-on-snow events. Cornices often catch people by surprise when they break farther back onto flatter areas than expected.
Aspects: North, North East, East, South East.
Elevations: Alpine, Treeline.
Likelihood: Unlikely
Expected Size: 1 - 1