Avalanche Forecast
Issued: Jan 27th, 2018 10:59AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Loose Wet.
NWAC,
Northwest Avalanche Center
A lull in this very active weather pattern will occur at Mt Hood Sunday allowing avalanche danger to decrease throughout the day. However, significant amounts of snow over the last two weeks deserve respect. Continue to travel cautiously avoiding steep open slopes where avalanches can initiate. Avalanches occurring Sunday may entrain additional snow, becoming larger and traveling farther than you might expect.
Summary
Detailed Forecast
A general warming trend will continue into Sunday for the Mt Hood region with occasional light showers. A break in precipitation will allow avalanche danger to decrease; however, this is not a time to let your guard down. Significant amounts of snow have fallen throughout the storm cycle. This much snow demands respect. Avoid steep open slopes where avalanches can start.
Near and above treeline wind slabs have grown large and destructive. Although they may become more difficult to trigger, a resulting avalanche will entrain additional snow becoming larger and traveling farther than you might anticipate.
Below treeline moist surface snow will still be able to produce loose wet avalanches. You are most likely to trigger these avalanches on steeper slopes. They may also be initiated by clumps of snow falling from trees and rocks. Although loose wet avalanches may be slower moving, they may push you into terrain traps where consequences of an avalanche are increased.
Snowpack Discussion
A long and stormy period has impacted the Mt Hood area since January 17th leaving 30 inches of settled storm snow over the most recent crust layer. Increased precipitation, warming temperatures, and strong winds combined Saturday to create very dangerous avalanche conditions and natural avalanches in many areas.
Rain Saturday morning formed thin breakable surface crusts up to 5500 feet before temperatures cooled and snow returned. Below 5500 feet a few inches of moist snow now sits above the breakable crust.
Winds throughout this active weather pattern redistributed snow forming deep and firm wind slabs on lee slopes near and above treeline.
With the ongoing storm cycle, direct observations above treeline have been hard to come by. A high level of uncertainty exists above treeline.
Observations
Mt Hood Meadows Patrol Satruday reported sensitive storm slabs which were entraining snow as they ran. A thin breakable rain crust formed in the morning to 5500 feet. By mid-day additional snow was falling at most elevations.
NWAC pro-observer Laura Greene was in the Newton Creek drainage Friday. She encountered low visibility with lots of new snow and wind transportation. Observations found 2.5 feet of storm snow.
On Wednesday, a professional ski patroller was caught, carried, and partially buried in an avalanche he triggered while on duty in a closed area of the Mt. Hood Meadows ski area (SS-AS-R2-D2-I). The avalanche released in an area known as God's Wall, running approximately 600 ft on the old/new snow interface. The bed surface was the firm 1/18 crust. Resources were dispatched immediately and the victim extricated after some difficulty due to low snow and open creeks. He was transported via ambulance to advanced care and is now discharged to recover from his injuries.
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 Wet
Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.
Several loose wet avalanches, and lots of pinwheels and roller balls.
Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.
Elevations: Treeline, Below Treeline.
Likelihood
Expected Size
Valid until: Jan 28th, 2018 10:59AM
