How to Apply the Avalanche Forecast to Your Riding
For splitboarders venturing into the backcountry, information can be the difference between an epic day and tragedy. In an effort to increase education and avalanche awareness, Spark R&D is presenting a 7-part web series called Avalanche Problems, which will explain the nationally standardized types of slides most commonly described in advisories by avalanche forecasters.
Understanding the characteristics of each type will help to determine where avalanches are likely to occur and what kind of terrain should be avoided. In today’s installment, we will cover Storm Slab Avalanches.
Storm slabs in a nutshell
Let’s face it: The best riding is often experienced during or right after a big storm. But in the backcountry, this can mean the new snow has formed a soft slab. The new snow may not be adhered to the underlying surface, or it may have an “upside down” structure. The best practice is to stay off of steep terrain (35 degrees and steeper) until the new snow has had time to adjust, which could take several days.
What exactly is a storm slab?
• A storm slab is new snow, which is cohesive enough to act like, or form a slab.
• Sometimes the slab is not bonding to the underlying surface. In other cases, it may form upside-down, meaning colder lighter snow on the bottom (weak layer) and heaver or wetter snow on top (slab). These tend to be smaller in size.
• If the storm snow is not a slab, than this is referred to as “loose dry” (next post). If a persistent weak layer is involved, than see the “persistent slab” problem.
• These are often short lived, and are experienced during or post storm event. The problem can last for several days, but can last longer if the temperatures remain very cold.
Where you might find a storm slab, and how to avoid them
• Storm slabs are typically widespread, but think about where the storm totals are greatest. Upper elevations, or the wet side of the range, are likely to have more of a problem.
• Higher elevations and shaded slopes are colder, which can preserve the problem for longer.
• Avalanches are more likely to occur in terrain 35 degrees or steeper. However, play it safe and stick to terrain under 35 degrees during or after the storm.
• Always be careful around natural avalanche paths during a storm, as start zones are becoming loaded and natural slides can occur.
How to look for and test a storm slab
• Hand pits and skin track cuts are nice tests if storm totals are under 1.5 feet (about 40cm), as they are very quick, can be done many times throughout the day, and give information on how well the snow is bonding. They allow you to look for patterns throughout the day.
• Ski cuts or stomps on steep slopes are great indicators for these surface conditions.
• Compression Tests (CT) are good for testing the bonding (lower scores or sudden planer sheers), and Extended Column Tests work if the new snow isn’t too soft.
Tips: If you get out for a few days in a row, watch for settlement cones around trees and bushes. Also, look for trends in your test scores: Higher scores, or more resistant hand sheers, mean the snow is starting to stick.
Disclaimer: Although characteristic, these descriptions are general, so make sure to read into any specifics mentioned on your local advisory. Also, this is just one piece of the puzzle, so remember to factor in the hazard rating and any field observations.
Find your local avalanche center: www.avalanche.org
Presented by Clark Corey
Splitboard Guide/Avalanche Educator