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Avalanche Forecast

Archived

Jan 18th, 2017–Jan 19th, 2017

Alpine
Natural avalanches unlikely, human triggered possible.
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 snowpack in the Olympics and Cascades is undergoing a lot of change and there is less than the usual certainty in which avalanche problems and danger levels to indicate. It might be a good plan to wait until Friday when conditions are better known and should be more stable.

Detailed Forecast

Winds and snow showers will decrease Wednesday night and Thursday with cooler temperatures.

Lighter storm snow should be seen above about 6000 feet at Mt Hood by Thursday.

New wind slab may be possible at higher elevations on the volcanoes where storm snowfall is heaviest. Underlying crusts may make wind slab sensitive on some slopes.

New storm slab will be most likely in any areas that experience rapidly accumulating snow of more than an inch an hour for several hours. Underlying crusts may make storm slab sensitive as well on some slopes.

The snowpack in the Olympics and Cascades is undergoing a lot of change and there is less than the usual certainty in which avalanche problems and danger levels to indicate. It might be a good plan to wait until Friday when conditions are better known and should be more stable.

Snowpack Discussion

Weather and Snowpack

An Arctic air mass was over the Northwest with fair, cold weather last week. Surface hoar and near surface faceted crystals probably formed in most areas during that period.

A drastic change was seen when an atmospheric river moved to the Northwest Tuesday and Wednesday. This caused rain up to about 7000 feet at Mt Hood.

Observations the next couple days should help determine to what extent any of the surface hoar and near surface faceted crystals from the fair cold weather might have survived the atmospheric river event.

Recent Observations

A couple reports for Mt Hood area available via the NWAC Observations page for last Thursday. A skier on the north side of Mt Hood noted E and W wind effects and potential wind slab in the near and above treeline. Another skier on Pea Gravel Ridge noted limited, thin wind slab near the top of the Ridge but otherwise snow was right side up and cornice and ski tests gave no results.

NWAC pro-observer Laura Green was touring in the east fork of Hood River up to 6100 feet on Friday. She found the upper snowpack generally non-reactive in snowpack tests with good skiing conditions especially below treeline. Good surface hoar growth was noted up to 6100 feet.

The Mt Hood Meadows pro-patrol on Wednesday reports that rain penetrated about 10 inches into the snow with no results during explosive avalanche control. Visibility was low on Wednesday and it could not be determined if there had been any natural avalanches on the upper mountain.

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.