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Avalanche Forecast

Archived

Mar 7th, 2016–Mar 8th, 2016

Alpine
Natural avalanches possible, human triggered probable.
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.

Be wary of unstable layers created during periods of rapid accumulation Monday that would make wind or storm slabs more likely to trigger. Persistent SW-W winds will continue to load lee slopes above treeline. Overall the potential for loose wet avalanches will decrease Monday and be confined to the lower elevations of the below treeline band and to steeper solar aspects that receive sunbreaks. 

Detailed Forecast

Light to locally moderate new snow received through Monday afternoon should accumulate at relatively cool and stable snow levels. 

Be wary of unstable layers created during periods of rapid accumulation Monday that would make wind or storm slabs more likely to trigger. Persistent SW-W winds will continue to load lee slopes above treeline. Overall the potential for loose wet avalanches will decrease Monday and be confined to the lower elevations of the below treeline band and to steeper solar aspects that receive sunbreaks. 

Cornices formed over the last week may still be weak from the recent mild weather so be aware of the overhead hazard and give cornices a wide berth while traveling along ridgelines. 

 

Snowpack Discussion

Weather and Snowpack

The last week has been wet and relatively mild with a series of active fronts transiting the region resulting in fluctuating freezing levels and periods of very strong winds (100+ mph gusts were not uncommon at the Cascade Express station).

The latter half of the week including the weekend has featured more rain than snow at NWAC sites on Mt. Hood. For perspective, the averaged freezing level measured in March thus far has been 6600 ft at Salem; more akin to spring than late winter.  

The mid and lower snow pack along the west slopes should be a stable mix of crusts and layers of moist and rounded snow crystals.

Recent Observations

The aftermath of the extreme wind event Tuesday was seen on Wednesday, with any exposed terrain stripped of recent snow, exposing a strong crust. The wind deposits were inconsistent and did not yield much in the way of avalanches, despite a healthy dose of bombs in the Mt Hood Meadows area. 

On Saturday, Mt. Hood Meadows pro-patrol reported wet snow up to about 6600' with a thin crust above and a well consolidated snowpack in their area. Following the cool down Saturday night, pockets of shallow new wind slab were seen above treeline in the Mt. Hood Meadows area by early Sunday morning. 

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.