Avalanche Forecast
Regions: Mt Hood.
Rainfall will renew the loose wet avalanche potential on all aspects of steeper slopes. New snowfall should bond well to a moist snow surface in most locations, but wind-driven snow may build unstable wind slab on lee aspects of higher terrain by Friday afternoon.
Detailed Forecast
Mild snow levels should keep precipitation in liquid form until a cold front passes through the Cascades Friday mid-afternoon with snow levels lowering to 5000 feet by late afternoon in the Mt. Hood area. Precipitation should be light in the morning and light to moderate in the afternoon.Â
Rainfall will renew the loose wet potential on all aspects of steeper slopes. New snowfall should bond well to a moist snow surface in most locations, but wind-driven snow may build unstable wind slab on lee aspects of higher terrain of Mt. Hood by late Friday afternoon.Â
Continue to watch for loose wet avalanche potential above terrain traps such as above cliffs, near gullies or where avalanche debris would deeply accumulate. These are the types of places that even small wet avalanches can have serious unintended consequences.
Avoid cornices along ridges and slopes below cornices since cornices may still be weaker due to the warm weather.
Snowpack Discussion
Weather and Snowpack
A large upper ridge and warm air mass aloft over the West Coast from this past Sunday through Wednesday led to the warmest weather of the winter. During this stretch temperatures were generally well above freezing. Freezing levels came down a few notches Thursday, but mild conditions continued with spotty light rain increasing Thursday afternoon in the Mt. Hood area.Â
The very warm temperatures and solar effects caused loose wet avalanches, snowpack consolidation, and melt-freeze surface crusts. This will have further stabilized the lower and mid snow pack and turned the most recent storm snow into moist to wet snow in most areas.Â
Recent Observations
Limited loose wet snow conditions were seen by Tuesday at Mt Hood by the pro-patrol. Moderate winds limited surface snow melt near and above treeline. More significant wet snow conditions were seen below treeline Tuesday with limited loose wet avalanche activity.
Small loose wet avalanches were reported as easy to initiate below 4600 feet Wednesday by Meadows pro-patrol, with similar conditions likely Thursday below treeline.
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: All aspects.
Elevations: All elevations.
Likelihood: Possible
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: North, North East, East, South East.
Elevations: Alpine.
Likelihood: Possible
Expected Size: 1 - 1