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Avalanche Forecast

Archived

Jan 16th, 2016–Jan 17th, 2016

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

Mt Hood.

Backcountry travel in avalanche terrain near and above treeline at Mt. Hood is not recommended on Sunday. Careful snowpack evaluation, cautious route finding and conservative decision-making will be essential below treeline.

Detailed Forecast

Another front will bring more moderate rain and snow to Mt. Hood Sunday, beginning in the early morning and turning to moderate showers in the early afternoon. 

This weather will generally cause upside down snow layers of increasing density near the surface and snow with rain likely below treeline in the morning. Up to about a foot of upside down snow should be seen by late Sunday afternoon.

New wind slab will continue to build mainly on lee north to east slopes near and above treeline. As the same lee aspects continue to load Sunday, very large avalanches will become possible. 

New storm slab due to the warming trend is also very likely on varied aspects where winds are lighter and snow rapidly accumulates to deeper than a few inches Avalanches releasing in near surface layers on Sunday may entrain previous snow producing large avalanches.

Small loose wet avalanche will again be likely in areas that see initial snow turn to rain Sunday, mainly on steeper slopes below treeline. 

Snowpack Discussion

The latest period of snowfall has been from about January 12-16th with up to about 2 feet at Mt Hood NWAC stations and fluctuating snow levels over this period.

A very active day on avalanche control was seen at Mt Hood Meadows Friday. The pro patrol reported explosively triggered widespread 1-4 foot slab avalanches on north to east slopes above treeline releasing on a crust from last weekend. Ski cuts were deemed to be too dangerous to undertake along with shooting cracks and some remote triggering by snow cats. Below treeline had storm slab and loose dry avalanches that were easy to trigger and running a more recent crust from about 2 days ago.

On Saturday, rain moved up to at least 6000 feet by late morning with snow levels lowering by mid-afternoon. Visibility was limited, but Meadows pro-patrol found 8-12" wet slabs very sensitive to ski cuts on steeper slopes below treeline. Steady winds continued to load lee aspects near and above treeline Saturday.  

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.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.