FWAC Education

This page contains some helpful resources for educating yourself on avalanche danger. Our Slope or Nope Model operates under the assumption that you will make informed decisions in the backcountry based on conditions you observe throughout the day. The concept of spatial variability, where snow stability changes dramatically over time and space, makes general predicting difficult so you must use your own observations to make the right call on the spot. In the following we provide some basic information and point you to good sources to education yourself further.

Basic elements needed for an avalanche

  1. Slab (load): Consolidated mass of snow
  2. Weak layer under slab that propagates instability over a distance
  3. Steep slope: Generally greater than 30 degree slope angle
  4. Trigger (deformation): e.g. weight of a human, cornice fall, etc.

Dangerous avalanche terrain characteristics (Tremper 2014)

  1. Is between 30-50 degrees (35-45 is most likely to slide)
  2. Has a wind load on it: leeward or cross-loaded.
  3. Has few anchors like trees.
  4. Has bad consequences if a slide occurs.

Safer avalanche terrain characteristics (Tremper 2014)

  1. Is gentle (0-25 degrees) or very steep (55+)
  2. Has densely spaced anchors
  3. Has less dangerous consequences if a slide occurs
  4. Is on the windward side of a slope.

Ways to limit risk during winter in the backcountry

Red Flags
Major indicators of instability that should prompt staying away from steep slopes:

  1. Wind intensity and direction: Generally greater than 19 kph (12 mph)
  2. Temperature above freezing for 24 hours
  3. Signs of avalanche: Recent avalanche activity.
  4. High rate of snowfall: Over 30 cm new snow in 24 hours.
  5. Whumpfing, cracking, collapsing (AIARE curriculum and Tremper 2013)

Yellow Flags
Five Structural Lemons

  1. Weak layer in top 100 cm of snowpack
  2. Weak layer thickness 10 cm or less
  3. Hand hardness difference greater than 1 step
  4. Weak layer grain type-persistent (SH, DH, FC)
  5. Grain size difference greater than 1 mm (McCammon & Schweizer 2002)

Some general rules of thumb from McClung & Schaerer (2009)

Stability Tests
A variety of tests exist to standardize the study of snow. Tests are only useful if they reveal instability. In other words, a test with no propagation score does not give a green light to enter avalanche terrain. The following are a list of resources for learning more about stability tests and their results:

Recommended readings

Tremper, B., 2014: Staying alive in avalanche terrain. Seattle (WA): The Mountaineers Books.

Tremper, B., 2013: Avalanche essentials: A step-by-step system for safety and survival. Seattle (WA): Mountaineers Books.

Ferguson, S. A., E. R. LaChapelle, and E. R. LaChapelle, 2003: The ABCs of avalanche safety. Seattle, WA: Mountaineers Books.

Know Before You Go: http://kbyg.org/


More technical resources

McClung, D., and Schaerer, P., 2006: The avalanche handbook. Seattle, WA: Mountaineers Books.

International Snow Science Workshop proceedings: http://arc.lib.montana.edu/snow-science/index.php?view=default

Snow, Weather, and Avalanche Guidelines: http://www.americanavalancheassociation.org/wp-content/uploads/2017/01/AAA_SWAG_Web.pdf