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Avalanche Forecast

Archived

Jan 26th, 2017–Jan 27th, 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.

The avalanche danger Friday should focus primarily on wet snow avalanches, especially on solar slopes during extended sunbreaks or filtered sunshine during the afternoon. Older wind slabs should be unlikely, but may linger near and above treeline on specific terrain features.   

Detailed Forecast

Sunshine or filtered sun through mainly high clouds is expected Friday with light winds and a continued warming trend.   

Watch for loose wet snow conditions on steep solar slopes during sun breaks or thin high clouds, especially during the warmest part of the day, Friday afternoon. 

With recent observations showing wind slabs bonding and stabilizing, we will lower the sensitivity to unlikely.   Any lingering older wind slabs will continue to strengthen and stabilize Friday. 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.

 

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 through Thursday produced about 1 to 4 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 the southeast slopes at about 6600 feet, finding right side up, increasingly resistant, 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.  

On Thursday, 1/26 Laura Green found very good bonding of the 1 foot of progressively resistant storm snow to the very strong 1/17 rain crust, This observation was at about 6300 feet on a south aspect. 

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.