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Avalanche Forecast

Archived

Feb 4th, 2016–Feb 5th, 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 unlikely, human triggered possible.

Regions

Mt Hood.

A mixed bag of ugly snow conditions and a high avalanche danger in the near and above treeline elevation bands is expected at Mt Hood on Friday. Backcountry travel in avalanche terrain especially in the near and above treeline bands is not recommended on Friday.

Detailed Forecast

The next weather system will move strongly to the Olympics and north Cascades Friday late morning and spread to the rest of the Cascades by Friday evening with fairly high snow levels.

A fairly broad brush will be applied to the avalanche forecast for Friday. Expect a mixed bag of ugly snow conditions and a high avalanche danger in the near and above treeline elevation bands at Mt Hood.

Wet snow and rain or warm temperatures should further build or activate wind and storm slab mainly in the above tree line band.

Recent snow will be available for activation by warm temperatures for potentially large loose wet avalanches at Mt Hood. Watch for surface wet snow deeper than a few inches and pinwheels or small natural loose wet avalanches that usually precede large loose wet avalanches.

But new snow and cooler temperatures should be seen by Saturday.

 

Snowpack Discussion

Weather and Snowpack

A strong occluded front crossed the Northwest last Friday and Saturday. NWAC stations on Mt Hood received about 1.5 feet of new snow

Cool and benign weather settled over Mt. Hood the last few days with ample sunshine on Tuesday.

A cold front crossed the Northwest on Wednesday. A warm front is causing heavy snow at Mt Hood today. NWAC stations at Mt Hood for the 2 days ending Friday morning will have about 1.5-2 feet increasing damp or wet upside down snow! 

Recent Observations

The Mt Hood Meadows pro-patrol today reported heavy snowfall and remotely and easily triggered widespread 1 foot wind slab mainly on north to southeast slopes along with storm slab in the near and above treeline. A combination of storm slab, loose wet avalanches and rollerballs was seen below treeline.

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.