Avalanche Forecast
Issued: Feb 23rd, 2018 11:21AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Storm Slabs.
NWAC,
Northwest Avalanche Center
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.
Summary
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
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.
Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..
Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.
Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Storm Slabs
Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. 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.
You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.
Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.
Elevations: Treeline, Below Treeline.
Likelihood
Expected Size
Valid until: Feb 24th, 2018 11:21AM
