Avalanche Forecast
Regions: Mt Hood.
Thursday's avalanche danger will consist of a mix of lingering wind slab near and above treeline and loose wet avalanches on solar slopes if extended sunbreaks materialize during the afternoon.
Detailed Forecast
Generally cloudy weather with light winds should be seen on Thursday although there may be some sunbreaks in the afternoon. A slow warming trend begins Thursday. Â
These conditions will continue to help recent wind and storm slabs settle and further stabilize. Lingering wind slabs may be found on a variety of aspects due shifting winds Tuesday night. Watch for recent wind effects near and below ridgelines and avoid steep slopes with obvious signs of recent wind loading.
Watch for loose wet snow conditions on steep solar slopes if the sun pops out for an extended period of time on Thursday afternoon.Â
Snowpack Discussion
Weather and Snowpack
An arctic air mass settled over the Northwest with fair, cold weather from the New Year through the second week of January. An atmospheric river moved over the Northwest 1/17-1/18 with heavy rain up to about 7000 feet on Mt. Hood during this stretch. Three day precipitation totals through Thursday 1/19 were about 1.5 - 2 inches of water at the NWAC Timberline and Meadows stations.Â
From last Thursday 1/19 through Sunday 1/22, generally 15-20 inches of snow accumulated at Mt Hood stations.
Fair weather with light winds and cool temperatures occurred Monday and Tuesday. A period of shifting and gusty winds Tuesday night helped redistribute recent snowfall to a variety of aspects by Wednesday morning. Light showers Tuesday night and Wednesday produced about 1 to 3 inches of new snow.Â
Recent Observations
On Monday, the pro-patrol at Meadows reported only pockets of stubborn wind slab above treeline on easterly aspects. This area had not been open or skied for 3 days and more closely represented true backcountry conditions.
NWAC pro-observer Matt Schonwald was at Timberline on Monday and on southeast slopes at about 6600 feet found right side up settled snow with a good bond to the 1/17 crust. Shallow wind slabs showed little tendency to propagate via ski tests.
Meadows pro-patrol reported isolated areas of shallow and soft wind slab up to 12" deep on a variety of aspects above treeline due to shifting winds Tuesday night. 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: 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: South East, South, South West.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 1