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Avalanche Forecast

Archived

Jan 18th, 2015–Jan 19th, 2015

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.

The avalanche danger at Mt Hood should gradually decrease on Monday. Watch for lingering wind and storm slab especially above treeline.

Detailed Forecast

Light west flow, light snow showers and slightly lower snow levels should be seen at Mt Hood on Monday. This should not build significant new layers. The avalanche danger should gradually decrease on Monday as new layers from Sunday partly stabilize.

Wind slab from Sunday should linger at Mt Hood mainly above treeline on Monday. It is also possible near treeline depending on if there is significant snowfall in this band on Sunday. Watch for firmer wind transported snow on previous lee slopes.

Storm slab from Sunday may linger to some extent at Mt Hood on Monday but will be stabilizing. Watch for cracking and releases on steep sheltered slopes where snowfall exceeded an inch an hour for more than a few hours on Sunday.

The cooling should also cause some good right side up snow conditions on other slopes on Monday.

Snowpack Discussion

Strong southwest flow carried a wet front across the Olympics and Cascades Saturday night. This front tapped subtropical moisture so snow levels got pretty high with about 3.5-4.5 inches of rain at NWAC sites at Mt Hood.

West southwest flow and mostly moderate showers are occurring at Mt Hood Sunday with slightly lowering snow levels.

NWAC observer CJ Svela was at Timberline on Sunday. He found consolidated P and 1F layers in the top meter of the snowpack. He reported about 8 cm of new snow at 7100 feet.

The mid and lower snowpack at Mt Hood should also mainly consist of melt-freeze crusts and stabilized rounded grain layers from warm periods so far this winter. Persistent weak layers are not expected at Mt Hood.

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.