Avalanche Forecast
Regions: Mt Hood.
It's the calm before the weekend storm: Friday's avalanche concerns should be limited to small and localized pockets of wind slab on lee aspects and small wet loose on solar aspects.
Detailed Forecast
An approaching Pacific frontal system should increase cloud cover for Mt. Hood late Friday afternoon and bring a significant uptick in SW winds. Significant new snow and rain should hold off until Friday night for Mt. Hood.   Â
The avalanche danger Friday should be limited to small and localized pockets of wind slab on lee aspects and small wet loose on solar aspects with both problems found mainly above treeline. Â
It's April, so be aware of the increased sun effects reaching more aspects and affecting the snow surface fairly quickly. Loose wet avalanches involving shallow amounts of recent storm snow will be possible, especially in any direct sun on solar slopes earlier in the day. Â
Cornices won't be highlighted as an avalanche problem due to the cool weather but use caution on slopes below cornices and on ridges where it can be hard to know if a cornice is present.
Snowpack Discussion
A large weak upper trough moved over the Northwest last weekend through early this week with showers Sunday depositing 6-7 inches at Mt. Hood. Freezing levels have been very low in April compared to most of the winter, averaging about 4-5000 feet. Shallow storm slab layer was reported by the Meadows patrol Monday.
On Wednesday and Thursday, clear skies transitioned to scattered afternoon showers with light and spotty new accumulations. The Meadows patrol reported easy shears in quick test pits in recent storm snow at 7300 feet on Wednesday on a lee aspect.Â
Snowpack problems at Mt Hood should remain in the upper or surface layers. The mid and lower snowpack at Mt Hood consists of layers of stable consolidated rounded grains or melt forms and crusts from multiple warm periods this season. Many areas at low elevations do not have enough snow to cause an avalanche danger.
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: Alpine, Treeline.
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, North West.
Elevations: Alpine.
Likelihood: Unlikely
Expected Size: 1 - 1