Avalanche Forecast
Issued: Mar 1st, 2018 10:03PM
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
You will be able to trigger avalanches in wind-loaded or steep open slopes at all elevations Friday. Recent wind and storm slabs may be found in many locations. While gradually stabilizing, these avalanche problems will need more time to heal. Stay off of open or wind-loaded slopes over 35 degrees and use travel routes and techniques to minimize your exposure to overhead avalanche terrain. Direct late-winter sunshine on steep sun exposed slopes may trigger shallow Loose avalanches.
Summary
Detailed Forecast
Cool temperatures and light winds are expected Friday with partly cloudy conditions and scattered light snow showers at times. This weather will allow for a gradually decreasing danger Friday. Any extended periods of direct late-winter sunshine may trigger shallow Loose avalanches on steep slopes facing the sun.
Fresh wind and storm slabs formed by early Thursday in many locations. While these slab layers continue to settle and stabilize, the cold temperatures will slow that process. It will still be possible to trigger these avalanches Friday.
Wind slabs may vary from soft to hard and are especially likely in higher exposed terrain below ridges that received wind deposited snow Wednesday night. The most likely aspects to encounter wind slabs are NW-SE facing terrain, though variations in local winds and cross loading of mid-slope features will require careful snowpack assessment. Identify and avoid steep slopes where the wind deposited snow. In some locations these wind slabs may be hidden by soft unconsolidated snow. Use visual clues such as cornices, the lack of snow in the trees, and large snow drifts to indicate wind loading on nearby slopes. Give this avalanche problem a wide berth Friday.
Wind slabs will have the potential to become large and destructive. Use travel routes and techniques to reduce your exposure to Mt Hood’s very large avalanche paths that originate higher on the mountain.
In wind sheltered locations, you will be able to trigger soft storm slabs up to 14” deep on open slopes greater than about 35 degrees. Storm slab layers are gradually healing but may still be possible to trigger Friday. Be patient as this active avalanche pattern proceeds.
Snowpack Discussion
About 8-10 inches of new snow was deposited by Thursday morning. Strong, mostly SSW winds accompanied Wednesday night's snowfall. This new snow fell on a variety of snow surfaces created during the last several days including crust on sunny aspects, wind featured snow, and unconsolidated surface snow in shaded sheltered areas.
In many locations more than 3’ of snow now sits on a firm buried crust layer (2/17). This crust has been reported up to 6600’ by professionals in the region. There are currently no significant layers of concern below the 2/17 crust.
Observations
On Thursday, Mt. Hood Meadows pro-patrol reported small to large slab releases reactive to ski cuts near and below treeline on steep slopes. Explosives above treeline released large to very large hard slab avalanches on many N-E facing terrain. These large slabs had crown faces ranging from 4-6 ft deep and produced significant avalanche debris in the runout zones well below the start zones!
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: Mar 2nd, 2018 10:03PM
