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Avalanche Forecast

Archived

Mar 25th, 2016–Mar 26th, 2016

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
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.

While recent storm related avalanche problems will have greatly diminished by Saturday, isolated areas of wind slab may remain on lee N through SE slopes near and above treeline. Also, loose wet avalanches will be possible on steeper solar slopes, especially if there are prolonged periods of sunshine.    

Detailed Forecast

Variable cloud cover on Saturday will be accompanied by generally light winds and rising freezing levels. An incoming frontal system arriving Saturday night should spread high clouds over the area in the afternoon. Mt. Hood may see more cloud cover than areas further north on Saturday which would limit the loose wet avalanche potential in this zone. 

Recent storm related avalanche problems will have greatly diminished by Saturday. Isolated areas of wind slab may remain on lee N through SE slopes near and above treeline, but should generally be stubborn to human triggering. Firm wind transported snow and snowpack cracking can be good signs of wind slab layers.

Loose wet avalanches will be possible on steeper solar slopes, especially if there are prolonged periods of sunshine. Be aware of terrain traps where even a small loose avalanche could have unintended consequences in the wrong terrain.    

Recently formed cornices have grown large. If traveling along ridgelines, be aware that cornices break much further back than expected and you don't want to go for a ride with a chunk of cornice. Despite the recent cool weather, cornice releases can be unpredictable during the spring.

Snowpack Discussion

Weather and Snowpack

A low pressure system crossed the Northwest on Monday and Tuesday. NWAC stations at Mt. Hood accumulated a few inches above 4000 feet during this time. Light rain was seen on Wednesday afternoon in the below treeline band before a cold front swept through Wednesday night with moderate to strong westerly transport winds continuing through early Friday morning.

Post-frontal snow accumulations Wednesday night through Friday morning varied based on elevation, with only a few inches below 5000 feet and about 8-10 inches at the Mt. Hood Meadows and Timberline stations. 

Frequent March storms have built large cornices along ridges in many areas.

The mid and lower snowpack along the west slopes should generally be a stable mix of crusts and layers of moist and rounded snow crystals.

Recent Observations

The Mt Hood Meadows pro-patrol on Tuesday morning 3/22 found wind loaded pockets of mostly small wind slab 12-18 inches deep in the above tree line which were stubborn to release by skis. On Tuesday afternoon a recent natural cornice release was seen at about 7000 feet on Marmot Ridge which released a small pocket of wind slab.

By Wednesday morning, Meadows pro-patrol found dense wind slab above treeline and on lee slopes only affected by large explosives. Above treeline, satstrugi was widely sculpted into the snow surface with some icy surfaces on windward ridges.  

Problems

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.

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.