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Avalanche Forecast

Archived

Jan 17th, 2016–Jan 18th, 2016

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

Regions

Mt Hood.

Even with an overall stabilizing trend on Monday, dangerous avalanche conditions will exist on lee wind-loaded slopes and where storm slabs remain sensitive to human triggering. Take it slow on Monday and evaluate the snowpack as you travel conservatively through the terrain.  

Detailed Forecast

Showers should taper off Monday morning and a few sunbreaks are possible mid-day before cloud cover increases Monday afternoon ahead of the next frontal system. 

Wind slab should be found mainly on lee north to east slopes near and especially above treeline. Very large avalanches are possible on lee slopes if initial releases are able to step down to a crust formed earlier this month. Generally avoid wind loaded slopes above treeline.  

Storm slabs may become more cohesive and likely to trigger with day-time warming and some sunshine. Choose lower angled slopes if you find sensitive storm layers.  

Small loose wet avalanches should be likely on steeper slopes below treeline involving small amounts of recent storm snow. Watch for loose wet avalanches near terrain traps, where even a small avalanche could have unintended consequences. 

Snowpack Discussion

The latest period of active weather from January 12-17th has accumulated about 3 feet of snow at both the Mt. Hood Meadows and Timberline Mt Hood NWAC stations. Fluctuating snow levels over this period has occasionally mixed rain up into the near treeline elevation band during this storm cycle.

A very active day on avalanche control was seen at Mt Hood Meadows Friday. The pro patrol reported explosively triggered widespread 1-4 foot slab avalanches on north to east slopes above treeline releasing on a crust from last weekend along with very sensitive ski cutting as well. 

On Saturday, rain moved up to at least 6000 feet by late morning with snow levels lowering by mid-afternoon. Visibility was limited, but Meadows pro-patrol found 8-12" wet slabs very sensitive to ski cuts on steeper slopes below treeline. Steady winds continued to load lee aspects near and above treeline Saturday. Another 0.50 - 1 inch of water on Sunday brought up to 6 inches of wet snow at Meadows and Timberline through 5 PM. 

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.