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Avalanche Forecast

Archived

Feb 24th, 2018–Feb 25th, 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.

New and reactive wind slabs will form Saturday on Mt Hood. Stay off of steep slopes at any elevation where winds are depositing snow and building fresh wind slabs. In sheltered areas, storm slabs may develop on open slopes over 35 degrees. Any avalanche occurring Saturday may entrain loose snow allowing it to grow large.

Detailed Forecast

Wind slabs will develop and build Friday night into Saturday as the next round of wind and precipitation impact the area. Expect avalanche conditions to worsen, with peak avalanche activity occurring during periods of strong winds and high snowfall rates.

Strong winds combined with snow available for transport will rapidly build new wind slabs on lee slopes and cross-loaded mid-slope features. Expect wind slabs to form on steep slopes below fresh cornices, blowing snow, and snow drifts. Use visual clues to identify and avoid any steep slope where winds are depositing snow. Wind slabs may exist well below ridgeline.

In sheltered areas, high snowfall rates may build new storm slabs. These will be most reactive during periods of peak snowfall intensity. New snow is falling on unconsolidated surface snow from earlier this week. You will be able to trigger storm slabs on slopes greater than 35 degrees.

Any avalanche occurring Saturday may entrain loose snow allowing it to grow large.

Snowpack Discussion

Loose surface snow conditions have been reported from the Mt Hood area over the last several days. As of Friday afternoon a generally right-side-up snowpack has been found in many locations. No new avalanches have been observed.

This light dry snow sits atop the most recent crust layer formed and buried on Saturday 2/17. This crust has been reported up to 6600 feet by professionals in the region. While many layers are present in the snowpack, avalanche problems and unstable snow will most likely be found in the new storm snow and it's interface with the old snow surface.

Observations

NWAC pro-observer Laura Green traveled in the Mt Hood backcountry Friday. Laura reported stable conditions prior to Friday’s incoming storm. She found a righ-side-up snowpack with loose unconsolidated surface snow.

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.