Large and destructive Wet Slab avalanches may occur above treeline. Avoid traveling on or below avalanche terrain originating at higher elevations. Avalanches may travel into lower elevation bands and reach valley bottoms. Stay off avalanche terrain where being caught in even a small Loose Wet avalanches could have dire consequences such as above cliffs, open creeks, or gullies.
Summary
Detailed Forecast
Continued warm and wet weather will maintain avalanche hazard in the Mt Hood area Saturday.
Above treeline areas will receive rain for the first time since early January. Rain falling on deep dry wind slabs may produce large and destructive slab avalanches. Wet Slabs are extremely difficult to predict. However, if they release they will entrain significant amounts of snow and travel into lower elevation bands. Avoid steep open slopes above treeline and limit your exposure to avalanche paths that originate at higher elevations.
Near and below treeline, rain on wet snow will maintain the possibility for Loose Wet avalanches. These avalanches are most likely during and following higher intensity rain showers. Avoid steep open slopes above terrain that could magnify the consequences of an avalanche. Cliffs, open creeks, rocks, and gullies are all examples of terrain traps where small avalanches may injure or kill you.
Snowpack Discussion
Warm wet weather has created wet surface snow conditions well into near treeline terrain in the Mt Hood area. At elevations receiving snow, SW winds continued to build wind slabs on lee slopes.
The upper snowpack consist of a mix of wet snow, old crust, and well consolidated storm snow. Observations demonstrate a strong and well bonded upper snowpack.
Observations
On Thursday, NWAC pro-observer Laura Green traveled in Newton and Heather Canyons. She found light rain beginning to wet the snow surface by mid-afternoon. Winds were increasing throughout the day.
On Wednesday, Mt Hood Meadows Pro Patrol reported the surface snow was sculpted by recent winds creating variable snow surfaces and scoured ridgelines. Below treeline, 6-8" of snow was well bonded to the 1/29 semi-supportable crust.
Mt Hood Meadows Pro Patrol Sunday reported multiple very large artillery-released avalanches with crowns up to 12 ft range, running on steep NE and ENE terrain above treeline and travelling very long distances, in one case snapping 20+ year old trees.
Problems
Wet Slabs
Release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slab avalanches can be very destructive.
Avoid terrain where and when you suspect Wet Slab avalanche activity. Give yourself a wide safety buffer to handle the uncertainty
A Wet Slab avalanche. In this avalanche, the meltwater pooled above a dusty layer of snow. Note all the smaller wet loose avalanches to either side.
Wet slabs occur when there is liquid water in the snowpack, and can release during the first few days of a warming period. Travel early in the day and avoiding avalanche paths when you see pinwheels, roller balls, loose wet avalanches, and during rain-on-snow events.
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.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Feb 3rd, 2018 10:00AM
