Dangerous avalanche conditions exist near and above treeline. Use extra caution in terrain steeper than 35 degrees and where you may be exposed to steep slopes from above. Very large and destructive wet avalanches and cornice falls are possible where heavy rain is falling on a previously dry snowpack.
Summary
Detailed Forecast
Expect dangerous and complex avalanche conditions today due to heavy rain and warming temperatures. Wet avalanches can be very large and can pose serious consequences. Avalanches big enough to bury a car are not out of the question today. The most dangerous slopes are near and above treeline. Previously dry snow above treeline will become saturated with water for the first time. Avoid slopes with a wet snowpack that are 35 degrees and steeper.
Wet Slab avalanches hold today’s gravest consequences. These avalanches are difficult to anticipate and manage. Use extra caution when crossing the tracks and runouts of avalanche paths and where you are exposed to overhead avalanche terrain. Wet Slabs could start at upper elevations and run long distances into lower elevations.
You are most likely to trigger or see Wet Loose avalanches. Many of these slides ran in the past couple days. The Wet Loose avalanche cycle is tapering off below treeline, but will continue at upper elevations. While these avalanches may be the smallest and most predictable of today’s problems, they could still be forceful or large enough to injure or bury you. Avoid traveling through or above terrain such as or cliffs, gullies, or rocky slopes where the consequences of being caught in an avalanche could be increased.
Cornice fall and Glide avalanches have become possible due to rain and rising temperatures. Both could be very large and dangerous. Avoid areas with visible glide cracks or where known rock slabs underlie the seasons snowpack. Give yourself an extra wide margin of safety near ridges that could hold cornices, and avoid slopes with cornices overhead.
Snowpack Discussion
Warm wet weather Friday and Saturday created moist to wet surface snow conditions up to 6500 feet. A natural Loose Wet avalanche cycle occurred Friday with peak warming and precipitation.
Above treeline, below freezing temperatures, additional snow, and moderate winds drifted snow on a variety of aspects. Poor visibility and stormy conditions have limited observations at higher elevations.
Cornices throughout the area have grown very large. Glide cracks have opened up on typical rock slabs especially in the Snoqualmie Pass and Mount Baker area.
Observations
Stevens Pass
NWAC Avalanche Forecasters and observers noted numerous natural wet loose avalanches on all aspects Friday and Saturday. These avalanches ranged from small to large, with some travelling 1000 vertical feet. As of Saturday rain created over 1 foot of wet surface snow, extending below the January 29th crust.
Snoqualmie Pass
On Saturday, Alpental Ski Patrol reported audible cornices collapses along ridges in the Alpental Valley. Both patrol and an NWAC observer reported Glide avalanches, visible glide cracks, and significant amounts of water running through the snowpack. Also reported were many wet loose avalanches at all aspects near and below treeeline
South
An avalanche professional in the Crystal backcountry Thursday noted lingering dry drifted snow near ridges. By late in the day light rain was already effecting the below treeline bands.
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, 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.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Feb 4th, 2018 12:11PM
