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Avalanche Forecast

Archived

Feb 3rd, 2016–Feb 4th, 2016

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

Wind slabs formed Wednesday, as well as expected continued wind transport Thursday, should maintain dangerous avalanche conditions, especially near and above treeline on a variety of aspects.

Detailed Forecast

Light to occasional moderate snow showers are expected Thursday with moderate WSW ridgetop winds. Moderate expected snowfall amounts and gradual warming should allow for settlement of storm related weaknesses. However, winds may still be strong enough to transport loose surface snow, continuing to deposit wind slabs on lee aspects, more NE-E-SE facing. Gradual warming Thursday may also make shallow storm slabs more sensitive during the day.

New snow may have initially bonded poorly to a variety of snow surfaces Wednesday, including weak lower density snow on sheltered and shaded slopes, or a possible thin sun crust on southerly facing slopes. Travel cautiously and make route choice decisions conservatively Thursday. 

Watch for signs of cracking or firmer wind transported snow.  Older and larger wind slabs may still be sensitive on similar aspects above treeline. 

 

 

Snowpack Discussion

Weather and Snowpack

A strong front crossed the Northwest on Friday, January 29th. NWAC stations on Mt Hood received about a foot of new snow by Saturday morning. About another 6-8 inches followed by Sunday morning. Cool and benign weather settled over Mt. Hood the last few days with ample sunshine on Tuesday.

The latest Pacific front arrived Wednesday afternoon, depositing about another 2-4 inches as of Wednesday evening, along with increasing strong winds. 

Recent Observations

On Sunday the Mt Hood Meadows patrol reported limited 4-6 inch wind slab on lee slopes in the above tree line, lower than usual below ridges, which would be small and difficult for a skier to trigger.

A report on Turns All Year, Sunday in Newton Canyon, indicated gradually harder compression tests with depth, in the right side up storm snow, with no signs of propagation.

The Mount Hood Meadows pro-patrol on Monday reported minor wind transport in the above treeline giving isolated, small pockets of wind slab. Also on Monday, NWAC pro-observer, Matt Schonwald found wind slab around 7000' on an ESE aspect in White River Canyon failing during snowpit tests at a density change 30-60 cm down. The slab was pencil hardness.  Matt found the wind slab hardness and sensitivity quickly diminished as elevations lowered. 

On Tuesday, the Meadows pro-patrol ventured well into their above tree-line terrain (Super Bowl). They found wind slab on lee aspects, failing at a density change 40-45 cm down, but not particularly reactive in snowpack tests.

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.