Avalanche Forecast

Archived

Apr 4th, 2018–Apr 5th, 2018

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

Mt Hood.

Stormy weather with rain will create dangerous avalanche conditions on Thursday. Wet heavy snow and wind will likely build new and reactive slabs. Avoid slopes steeper than 35 degrees where you can trigger Wind Slab avalanches. Expect that you can trigger wet avalanches on slopes receiving rain.

Detailed Forecast

Snow, wind, and rain are combining to create dangerous avalanche conditions. Warm, wet weather is building new slabs at upper elevations and soaking snow surfaces near and below treeline. Wind has drifted slabs on lee slopes above treeline. In some locations, these new slabs will overly lower density snow from earlier in the week. Visual clues such as blowing snow, fresh cornices, and cracks in the snow all indicate you could trigger a Wind Slab avalanche.

Near and below treeline, rain has set the stage for wet avalanche conditions. As the rain line moves up in elevation, expect natural Loose Wet avalanches especially near treeline. If water reaches buried crusts or softer layers of snow, Wet Slab avalanches could occur. Wet Slabs can be hard to predict and very destructive. If you see slab avalanche activity during periods of rain, avoid traveling in avalanche terrain.

Snowpack Discussion

Light snow changed to light rain on Mt Hood Wednesday beginning the transition to wet snow conditions at mid and lower elevations. Some shallow new drifts may have formed above treeline in exposed wind affected terrain.

In general 12-14 in. (30-35 cm) of new snow fell in the Mt Hood area Sunday and Monday. Strong westerly winds during the storm and through the day Tuesday redistributed much of the recent snow at higher elevations, forming wind slabs on lee slopes. The new snow fell on a firm melt-freeze crust in many locations forming an initially poor bond. Wind slabs were less reactive to human triggers Tuesday, but still producing 1-3 ft avalanches with explosive control above treeline, mainly on N-E facing slopes.

The recent 1 ft plus of snow has settled and stabilized below treeline as of Tuesday where there were no reported avalanches.

There are currently no significant layers of concern in the mid or lower snowpack.

Observations

No avalanches were reported Wednesday.

Tuesday, Mt Hood Meadows pro patrol reported Wind Slabs releasing with explosives on N-E lee slopes above treeline, averaging 1 ft. Wind Slabs were no longer sensitive to ski trigger. Below treeline, storm layers had settled and stabilized with no avalanches reported near or below treeline.

On Monday, Mt Hood Meadows ski patrol reported 1-2 ft (30-60cm) Wind Slab avalanches on lee slopes above treeline during control work. Near treeline, 6-12 inch (15-30cm) Wind Slabs were triggered on wind loaded slopes. Below treeline the 12-14 inches (30-35cm) of recent storm snow lacked slab properties, however Dry Loose avalanches were possible.

Problems

Wind Slabs

Wind Slab avalanches are the 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.

Loose Wet

Loose Wet avalanches are the 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. 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.