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Avalanche Forecast

Archived

Feb 14th, 2017–Feb 15th, 2017

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

Back country travel will require cautious route finding and careful snowpack evaluation at Mt Hood on Wednesday.

Detailed Forecast

Strong southwest flow aloft will carry a very moist frontal system to the Northwest on Wednesday. This will cause stormy wet weather along the Cascade west slopes on Wednesday with rain and high snow levels. The most rain should be seen in the Washington Cascades. See the NWAC Mountain Weather Forecast for details.

Dangerous avalanche conditions are possible at Mt Hood on Wednesday. Natural or triggered loose wet and wet slab avalanches are possible on Wednesday depending on how much rain there is, how it percolates into the snowpack and if avalanches entrain deeper layers.

Observations and tests for loose wet avalanches are more straightforward such as wet surface snow deeper than a few inches, rollerballs and natural loose wet avalanche actiivity.

But observations and tests for wet slab avalanches are more difficult since it is usually hard to know the effects of significant amounts of water percolating into the snowpack.

Cautious route finding and careful snowpack evaluation will be required if you decide to travel in the back country at Mt Hood on Wednesday.

 

Snowpack Discussion

Weather and Snowpack

The aftermath of the last storm cycle 2/8-2/10 left a very strong rain crust with whatever amount of new snow received above, except for areas exposed to west winds which remained scoured to the firm and slick crust.  

High pressure Saturday to Tuesday brought increasing sunshine and warm temperatures. Temperatures reached the 40's and 50's in many areas of the Olympics and Cascades by Monday and Tuesday. This caused a lot of snowpack settlement, some small loose wet avalanche activity and a decreasing avalanche danger.

Recent Observations

A very large 6-8 foot slab avalanche released sometime last week likely 2/8-2/10 from about the 8000 foot level in Newton Canyon.

On Friday 2/10 the 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.

Otherwise the Meadows pro-patrol reported only some rollerballs and no significant avalanche activity on Monday and Tuesday.

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.

Wet Slabs

Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.