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Avalanche Forecast

Archived

Feb 12th, 2017–Feb 13th, 2017

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.

Watch for melting and weakening surface snow on steep sun exposed slopes where loose wet avalanches will be possible. Continue to be cautious in steep previously wind loaded terrain or any features showing signs of wind deposited snow. 

Caution travelling on steep slopes with a slick crust.

Detailed Forecast

Sunshine and very mild temperatures with light to moderate ridgetop winds are expected Monday. Freezing levels should near 10,000 feet Monday.  

Older wind slabs should have settled and stabilized by Monday, but watch for signs of wind deposited snow on specific terrain features such as steep slopes below ridges.

Sunshine and very mild temperatures Monday should make loose-wet avalanches possible on steep southerly slopes facing the sun. Be cautious on sun exposed slopes if the wet surface snow becomes more than a few inches.   

Some slopes exposed to recent winds or where less new snow was received after rain changed to snow, may have an exposed very slick crust. Be cautious of uncontrolled falls and avoid traveling on steep slopes with slick crust in terrain of consequence. 

Snowpack Discussion

Weather and Snowpack

A strong storm cycle Friday, 2/3 through Monday 2/6 deposited about 3-4 feet on Mt Hood. 

Things changed in a hurry as strong SSW flow brought a series of storms with heavy rain to the Mt Hood area Wednesday afternoon through Thursday. About 2 inches of water fell mainly as rain on Mt. Hood from by Thursday afternoon with significant snowpack settlement. A strong cold front passed Thursday afternoon, followed by bands of light showers in SW flow along with the start of a slow cooling trend.  

Friday was windy with a slow cooling trend during the day. Light to moderate snow showers deposited about 6-8 inches of new snow by Saturday morning. 

Sunshine and warming Sunday allowed for temperatures to reach the 40's at most NWAC stations by Sunday afternoon. This allowed for further stabilization of any new snow layers and caused additional settlement and a decreasing danger. 

Recent Observations

On Thursday, Meadows pro-patrol reported saturated snow down 25 cm but no avalanche activity in the ski area. The upper mountain was not observed due to strong winds and limited visibility. 

By Friday morning Meadows pro-patrol reported widespread loose-wet and small wet slab, natural activity had occurred Thursday near and above treeline. One very large wet slab occurred in the God’s Wall path up to size D3, likely releasing sometime Thursday.  Below treeline, a saturated snowpack was still re-freezing and became less supportable at lower elevations.  

By Saturday the old wet snow had formed a variable crust, ranging from supportable to breakable in spots. 

By Sunday a very strong and supportable rain crust lies beneath the settled 6-8 inches of surface snow.

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.