Avalanche Forecast
Regions: Mt Hood.
The avalanche danger will increase during the day on Thursday with very windy conditions quickly forming fresh Wind Slabs. Look for developing Wind Slabs on lee slopes near and above treeline that you can easily trigger. Rainfall will increase the likelihood for Loose Wet avalanches below treeline. The avalanche danger will increase further Thursday night.
Detailed Forecast
The avalanche danger will increase during the day on Thursday as a storm system brings light to moderate rain and snow to Mt. Hood along with very windy conditions. Look for developing Wind Slabs on lee slopes near and above treeline that you can easily trigger. Watch for cracking, wind stiffened snow, and freshly formed drifts. Steer around fresh wind features, convex rolls, and slopes holding a foot or more of new, cohesive snow that are 35 degrees and steeper. Shallow Storm Slabs may develop by the afternoon in wind sheltered terrain. The avalanche danger will continue to increase Thursday night.Â
The rain/snow line is forecast to rise to 5000-5500' Thursday. Rainfall will raise the likelihood of small Loose Wet avalanches on steep slopes below treeline, especially those that have received fresh snowfall. Avoid steep slopes below treeline connected to terrain traps, where even a small Loose Wet avalanche could have unintended consequences.Â
Snowpack Discussion
Temperatures were above freezing at NWAC stations at Mt. Hood Wednesday. Combined with overcast skies, this likely moistened the snow surface on all aspects near and below treeline. Loose Wet avalanches were reported Tuesday on sunny aspects.Â
Mt. Hood received 3" of new snow Sunday night through Monday morning and west winds were transporting snow onto lee slopes (mostly easterly aspects) forming shallow wind slabs about 8" deep.
In many locations more than 3’ of snow now sits on a firm buried crust layer (2/17). This crust has been reported up to 6600’ by professionals in the region. There are currently no significant layers of concern below the 2/17 crust.
Observations
NWAC pro-observer Laura Green was in Mitchell Creek Monday and observed active wind loading occurring near and above treeline. No new or recent avalanches were observed.
On Monday, Mt. Hood Meadows Pro Patrol reported west winds transporting snow, 8" of new and generally non-reactive wind slab on lee aspects limited to E facing slopes. Winds eased mid-day. Small loose wet avalanches occurred on solar, especially below treeline.
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: 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: Below Treeline.
Likelihood: Likely
Expected Size: 1 - 1