Avalanche Forecast
Regions: Mt Hood.
Moderate and persistent crest alpine winds out of the northeast Monday night and Tuesday will redistribute recent snowfall to unusual aspects mainly above treeline. At lower elevations and in wind sheltered terrain, the main avalanche problem will shift from wind slab to loose wet due to sunny skies and warming temperatures.
Detailed Forecast
Moderate and persistent alpine winds out of the northeast Monday night and Tuesday will redistribute recent snowfall to unusual aspects mainly above treeline. At lower elevations and in wind sheltered terrain, the main avalanche problem will shift from wind slab to loose wet due to sunny skies and warming temperatures. Â
A mix of older wind slab on lee easterly aspects and new wind slab on south through westerly aspects will make wind slab avalanches possible on a variety of aspects, and ultimately for tricky and dangerous travel above treeline Tuesday. Watch for cracking and firmer or chalky wind transported snow. Yesterday's windward aspect may be today's loaded lee slope.Â
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. Moderate winds near and above treeline will limit the loose wet potential except on direct solar slopes. Be aware of terrain traps where even a small loose wet avalanche could have unintended consequences. Â
Near treeline should be a mix of loose wet avalanche and wind slab concerns. Â
Cornices have grown large recently. 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 last Wednesday to Friday 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
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.  A nice example of a reactive wind slab was found in the Timberline area Monday. A 10" wind slab of denser snow released with a ski cut during warming Monday.Â
Photo 3-28-16 by Alex Laudon, Timberline 6200 ft SE aspect
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: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible
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: All elevations.
Likelihood: Possible
Expected Size: 1 - 1