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Avalanche Advisory for 2017-04-16 06:33:48

  • EXPIRED ON April 17, 2017 @ 6:33 am
    Published on April 16, 2017 @ 6:33 am
  • Issued by Andrew Kiefer - Mt Shasta Avalanche Center
  • April 16, 2017 @ 6:33 am

    Advisory Hotline: (530) 926-9613

  • The Mount Shasta Avalanche Center has closed its doors for the 2016-2017 winter season. We will resume issuing daily avalanche advisories in the fall of 2017.

    The climbing rangers will be updating the Overall Climbing Conditions and Climbing Route webpages throughout the 2017 climbing season. Avalanche activity will likely continue to occur this spring throughout the advisory area. For an overview of the most common springtime avalanche concerns, please read the full spring avalanche statement below.

Avalanche Problem 1: Loose Wet

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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

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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

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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.

Advisory Discussion

Spring Statement 2017

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 snowpack is deep and strong, 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!

Recent Observations

We will update the Observations section of our webpage if there are significant avalanche, snowpack, and weather events this spring. If you gather observations out in the field, send them our way! You can post your observations by clicking the blue tabs labeled Submit Snowpack/Avalanche Observations.

THIS SEASON PRECIPITATION for MT SHASTA CITY: From October 1, 2016 through April 16, 2017 we have received 56.44 inches of water, normal 37.07 inches putting us at 152% of normal.  For the month of April, we have received 6.98 inches of water, normal is 1.61 inches, which is 434% of normal. And finally for the year of 2017, we have received 35.28 inches of water, normal is 21.86 inches, putting us at 161% of normal.

Current Conditions at Bunny Flat (6950')

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Weather

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.

Two Day Mountain Weather Forecast

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Disclaimer

This advisory does not apply to Ski Areas or Highways and is for the Mt. Shasta, Castle Lake and Mt. Eddy backcountry. Use this information for guidance only. You may find different conditions in the backcountry and should travel accordingly. This advisory expires on midnight of the date it was posted unless otherwise noted.