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Avalanche Forecast

Archived

Feb 16th, 2018–Feb 17th, 2018

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.

Regions

Mt Hood.

Avoid steep open slopes at all elevations where you will be likely to trigger an avalanche Friday. Snow and wind throughout the day will cause avalanches to become larger and easier to trigger. Conservative decision making will be essential for safe travel.

Detailed Forecast

Additional snow and wind Friday will cause the avalanche danger to increase throughout the day. Expect changing conditions as avalanche problems become easier to trigger.

Identify and avoid steep wind loaded terrain and mid-slope crossloaded features. Visual clues such as blowing snow, plumes, and fresh cornices signal wind slabs exist on slopes below. Some of these avalanches will be large and may propagate widely. Give wind loaded terrain a wide berth Friday.

As the storm totals grow, you will be more likely to trigger storm slab avalanches. Storm slabs exist on all aspects. Avoid open slopes greater than 35 degrees where you will be likely to trigger a storm slab.

Snowpack Discussion

Winds at Mt Hood have significantly redistributed the recent storm snow forming a variety of surfaces near and above treeline. Scoured surfaces can be found on windward slopes, while lee sloped hold 2-4 feet of wind deposited snow. In sheltered areas 10-12 inches storm snow fell Wednesday onto a strong firm crust layer. Soft subtle storm slabs have formed with settlement of the new snow.

The recent snow sits on top of a firm crust layer formed on Feb 8th. The warm wet weather from the beginning of February created a strong consolidated snowpack. There are no significant layers of concern in the mid and lower snowpack.

Observations

NWAC professional observer Laura Green and the Mt Hood Meadows ski patrol Thursday reported wind transported snow near and above treeline. Wind scoured slopes were reported on windward aspects. Deep wind slabs up to 6 feet were observed during avalanche mitigation work Thursday 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.