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Avalanche Forecast

Archived

Jan 25th, 2017–Jan 26th, 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.

Thursday's avalanche danger will consist of a mix of lingering wind slab near and above treeline and loose wet avalanches on solar slopes if extended sunbreaks materialize during the afternoon.   

Detailed Forecast

Generally cloudy weather with light winds should be seen on Thursday although there may be some sunbreaks in the afternoon. A slow warming trend begins Thursday.  

These conditions will continue to help recent wind and storm slabs settle and further stabilize. Lingering wind slabs may be found on a variety of aspects due shifting winds Tuesday night. Watch for recent wind effects near and below ridgelines and avoid steep slopes with obvious signs of recent wind loading.

Watch for loose wet snow conditions on steep solar slopes if the sun pops out for an extended period of time on Thursday afternoon. 

Snowpack Discussion

Weather and Snowpack

An arctic air mass settled over the Northwest with fair, cold weather from the New Year through the second week of January. An atmospheric river moved over the Northwest 1/17-1/18 with heavy rain up to about 7000 feet on Mt. Hood during this stretch. Three day precipitation totals through Thursday 1/19 were about 1.5 - 2 inches of water at the NWAC Timberline and Meadows stations. 

From last Thursday 1/19 through Sunday 1/22, generally 15-20 inches of snow accumulated at Mt Hood stations.

Fair weather with light winds and cool temperatures occurred Monday and Tuesday. A period of shifting and gusty winds Tuesday night helped redistribute recent snowfall to a variety of aspects by Wednesday morning. Light showers Tuesday night and Wednesday produced about 1 to 3 inches of new snow. 

Recent Observations

On Monday, the pro-patrol at Meadows reported only pockets of stubborn wind slab above treeline on easterly aspects. This area had not been open or skied for 3 days and more closely represented true backcountry conditions.

NWAC pro-observer Matt Schonwald was at Timberline on Monday and on southeast slopes at about 6600 feet found right side up settled snow with a good bond to the 1/17 crust. Shallow wind slabs showed little tendency to propagate via ski tests.

Meadows pro-patrol reported isolated areas of shallow and soft wind slab up to 12" deep on a variety of aspects above treeline due to shifting winds Tuesday night.  

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.