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Avalanche Advisory for 2018-04-15 05:02
- Issued by Aaron Beverly - Mount Shasta Avalanche Center
Avalanche Problem 1: Loose Wet
Loose wet avalanches will be the primary avalanche concern throughout the spring on Mount Shasta. Loose wet avalanches are the release of wet, unconsolidated snow or slush. They start at a point and entrain snow as they move downslope, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Some of these avalanches may seem harmless, but can be deadly in high consequence terrain like above cliffs or a terrain trap. It is also important to remember that wet loose avalanches can trigger slab avalanches that break into deeper snow layers.
Travel when the snow surface is colder and stronger. Typically, this involves starting early and heading back early. Plan your trips to avoid crossing on or underneath very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushy. Avoid steep, sunlit slopes above terrain traps, cliffs and long sustained steep pitches.
Avalanche Problem 2: Storm Slab
Springtime storms can often produce heavy precipitation, rapidly adding new snow and weight to the snowpack. It is important to give the snowpack time to adjust after a significant snowfall, as storm slab problems can last for a few hours to a few days. Storm slabs are the release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Often in the spring, new snow will fall on melt-freeze crusts (sun or rain crusts). These crusts provide a great bed surface for the new snow to slide on.
You can reduce your risk of getting caught in a storm slab avalanche by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps like gullies, cliff bands, dense timber, or terrain features that make it difficult for a rider to escape off the side.
Avalanche Problem 3: Wind Slab
Large storms accompanied by strong winds are likely to occur this spring. Winds slabs form during storms, for several days following a storm, and during high wind events. Pay attention to wind direction and how the wind transported snow is redistributed throughout the terrain. Use clues like blowing snow, cornice formation, and textured snow surfaces to identify areas where potentially unstable wind slabs exist. Look for typical signs of mid winter instability like recent avalanches, shooting cracks, and/or whumphing.
Spring Statement 2018
Conditions in the mountains can change rapidly in the springtime. The full spectrum of weather is possible, and several different avalanche problems can arise in the backcountry. The problems listed above are the most likely this coming spring, but cornice fall, wet slab, and glide avalanches are additional concerns to keep in mind as the snowpack continues to transition over the next few months.
More snow and cold temperatures are likely to continue this spring. Fortunately, our existing snowpack is strong and stable, which means instabilities to come will likely only involve new snow layers at the snow surface. The majority of storm slab and wind slab avalanches that may occur this spring are likely to happen during or immediately following big snowstorms. Make sure to give the snowpack time to adjust after it snows before committing to complex avalanche terrain.
For most days throughout the spring, a diurnal melt-freeze cycle will dictate the avalanche hazard. With clear dry weather conditions, snow surfaces often freeze overnight and thaw during the day. When snow surfaces are frozen, snowpack stability is at its best. As they thaw, the snowpack looses strength and stability can become poor, often with increasing avalanche danger by late morning and afternoon. Loose wet avalanche activity should be expected during these weather conditions. Falling rime ice and rock fall also pose major hazards to climbers and skiers in alpine terrain on Mount Shasta. Melt-freeze cycles affect these hazards as well, and timing and efficiency are critical if you choose to expose yourself to terrain threatened by ice fall and rock fall.
In addition to rapid warming due to temperature and solar radiation, rain on snow is a major red flag for avalanches. Rain can work especially quickly to destabilize the snowpack, and rain on snow events are likely in the coming months. Not only can these factors produce wet loose avalanches, but can lead to wet slab and glide avalanches as well. Wet slab and glide avalanches often occur with prolonged periods of non-freezing temperatures and/or heavy rainfall. As free water percolates down through the snowpack, it can weaken deeper layers of snow or even the entire snowpack. If free water encounters a crust, ice lens, or smooth ground surface, it may flow along the interface and lubricate it, making avalanches increasingly likely within the snow above.
Regardless of whether the snow keeps falling or not, avalanches can and will likely occur until the existing snowpack melts away. Do not let your guard down, and be sure to evaluate the changing snowpack conditions.
Finally, we would like to extend a huge thank you to all who have helped support the Mount Shasta Avalanche Center. Your observations, donations, feedback, and general support are very much appreciated. Thank you for a great season and we will see you back here next winter!
We will update the Observations section of our webpage if there are significant avalanche, snowpack, and weather events this spring. We will also be extending our observations to include climbing route and trailhead conditions. Look for these on the home page, in the climbing advisory, and on climbing route and trailhead descriptions. If you gather observations out in the field, send them our way! You can post your observations by clicking the blue tabs under listed observations.
Weather and Current Conditions
Please check our Weather tab at the top of the page for our remote weather station information, NWS Forecast Discussion, NWS Recreational Forecast, and point forecasts.
ALWAYS check the weather before you attempt to climb or recreate on Mount Shasta. Continue to monitor the weather as you climb. Becoming caught on the mountain in any type of weather can compromise life and limb. Please be prepared.