Avalanche Forecast
Issued: Feb 14th, 2018 10:12AM
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
Avoid steep slopes near ridgelines and cross-loaded features where winds have formed new and sensitive wind slabs. Use visual clues such as blowing snow, fresh cornices, snow drifts, and uneven snow surfaces to identify slopes with wind deposited snow.
Summary
Detailed Forecast
You will be able to trigger wind slab avalanches on lee and cross-loaded slopes near and above treeline Thursday. Avoid steep slopes where the wind is depositing snow. Blowing snow and plumes are easy observations that wind slabs exist nearby. Use visual clues to help you actively identify and avoid wind slabs below ridges and on mid-slope features.
Loose surface snow from Wednesday will begin to settle making it possible for you to trigger small storm slabs. Stay away from convex rollovers, very steep slopes, and unsupported terrain where you are more likely to trigger a slab avalanche.
The new storm snow is poorly bonded to the old icy snow surface. Small loose dry avalanches (sluffs) are not listed as a problem but will be possible until this bond improves. Avoid terrain where even small avalanches could have higher consequences such as above cliffs, rocks, and creeks.
Snowpack Discussion
Around a foot of new snow fell in the Mt Hood area Wednesday. Moderate to strong westerly winds quickly redistributed the new snow forming wind slabs on lee slopes and cross-loaded mid-slope features. Wind slabs continued to grow throughout the day.
In sheltered areas the snow bonded poorly to the old snow surface. Loose surface conditions were reported with no slab development in the new snow.
Below Wednesday’s storm snow a strong and well consolidated snowpack exists. . Unstable snow should be limited to the new snow and its bond with the old snow surface. There are no significant layers of concern in the mid and lower snowpack.
Observations
On Wednesday Mt Hood Meadows ski patrol reported winds actively transporting storm snow near treeline. Wind slabs were observed on mid-slope cross-loaded features. In sheltered areas small loose dry avalanches were seen.
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: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
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.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Feb 15th, 2018 10:12AM
