Avalanche Forecast
Issued: Jan 28th, 2018 11:53AM
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
Dangerous avalanche exist at upper elevations due to recent wind loading. Use extra caution near or below any large avalanche paths. You can trigger very large and destructive avalanches on Monday.
Summary
Detailed Forecast
The warm sector of the storm will be over the Mt. Hood area on Monday with a break in the storm continuing for another day, further allowing recent very large wind and large storm slabs time to heal. 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 are very large and have proven destructive. The largest of these slabs may require a very large trigger such as a cornice and will be very large in size. Any avalanche will entrain additional snow, becoming larger and travel farther than you might anticipate. Avoid avalanche terrain where avalanches my start, run, or stop. Rain on Sunday morning should have reduced the danger of triggering a wind slab near treeline.
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. 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 relative break in the action was seen from late morning onward on Sunday after a long and stormy period which has impacted the Mt Hood area since January 17th leaving 30 inches of settled storm snow over the most recent crust layer. Saturday and Sunday featured more intense precipitation, significant warming temperatures, and strong winds created very dangerous avalanche conditions and natural avalanches in many areas.
The break in the weather allowed good visibility of multiple very large artillery-triggered wind slabs which entrained lots of wet snow and even in one case knocked down timber.
Rain on Saturday morning was followed by cooling, creating a thin, breakable crust in some areas.
Winds throughout this active weather pattern redistributed snow forming deep and firm wind slabs on lee slopes near and above treeline.
Observations
Mt Hood Meadows Pro Patrol Sunday reported multiple very large artillery-released avalanches with very deep crowns in the 10-20 ft range, running on steep NE and E-NE terrain above treeline and travelling very long distances, in one case snapping 20+ year old trees.
Mt Hood Meadows Patrol Saturday 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.
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 29th, 2018 11:53AM
