Avalanche Forecast
Issued: Feb 22nd, 2018 11:32AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Loose Dry.
NWAC,
Northwest Avalanche Center
New shallow wind slabs will build during the day on Friday above treeline. You will most likely be able to trigger these avalanches on steep slopes near wind drifting and blowing snow, and below fresh cornices. In sheltered areas, loose snow conditions will continue. Avoid steep slopes where even small loose dry avalanches can have larger consequences such as above cliffs, creeks, and gullies.
Summary
Detailed Forecast
New shallow wind slabs will form Friday, especially above treeline, as the next round of precipitation and wind begins to impact Mt Hood in the afternoon. The avalanche danger will rise slightly throughout the day as slabs grow deeper and become easier to trigger. Look for areas of wind blowing snow, plumes, fresh cornices, and drifting snow. Avoid steep slopes where wind deposition is occurring.
In sheltered areas, loose surface snow will exist. You will be most likely to trigger loose snow avalanches on slopes greater than 35 degrees. Avoid slopes with higher consequences such as above cliffs, gullies, and creeks where even small avalanches can harm you.
Any avalanche occurring Friday will have the potential to entrain loose surface snow and grow large.
Snowpack Discussion
Several natural loose dry avalanches were reported Wednesday on slopes steeper than 35 degrees. These avalanches resulted from snow falling with generally cold temperatures and light winds creating loose snow surface conditions at all elevations. The Mt Hood area has received several feet of light dry loose snow over the last several days. Little to no slab formation has been reported in the recent snow.
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, unstable snow has been relegated to the upper few feet.
Observations
On Wednesday, professional observations from the Mt Hood Meadows area indicated Loose-Dry avalanches were possible in steep terrain with several small natural Loose-Dry releases seen.
On Monday, Mt Hood Meadows patrol traveled into the above treeline area for the first time since the strong storm cycle. Surprisingly, they found a lack of wind slabs in terrain usually laden with them. The very cold temperatures may have limited slab formation in this area.
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: Alpine, Treeline.
Likelihood
Expected Size
Loose Dry
Release of dry unconsolidated snow. These avalanches typically occur within layers of soft snow near the surface of the snowpack. Loose Dry avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs. Loose Dry avalanches can trigger slab avalanches that break into deeper snow layers.
Loose Dry avalanches are usually relatively harmless to people. They can be hazardous if you are caught and carried into or over a terrain trap (e.g. gully, rocks, dense timber, cliff, crevasse) or down a long slope. Avoid traveling in or above terrain traps when Loose Dry avalanches are likely.
Loose Dry avalanche with the characteristic point initiation and fan shape.
Loose dry avalanches exist throughout the terrain, release at or below the trigger point, and can run in densely-treed areas. Avoid very steep slopes and terrain traps such as cliffs, gullies, or tree wells.
Elevations: Treeline, Below Treeline.
Likelihood
Expected Size
Valid until: Feb 23rd, 2018 11:32AM
