San Francisco Peaks / Kachina Peaks Wilderness

Avalanche problems

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  2–3

  The addition of new snow ( 49 inches in 60 hours), adding more stress to the snowpack, has increased the likelihood of persistent slab avalanches. Areas with a thin snowpack (<100cm) pose the largest risk for triggering a persistent avalanche, as it is easier for a traveler's weight to collapse the depth hoar at the base of the snowpack. Typically warning signs such as shooting cracks and whumpfing may not occur until it is too late.  Anticipate that these avalanches will grow wider and run further than you expect, yielding a high-consequence scenario that could bury, hurt, or kill a backcountry traveler.

  For example, the very large natural avalanche on the NE face of Fremont in early January had a max crown height of 2 meters and destroyed 30-40-year-old trees. Additionally, a second large natural avalanche occurred in Abineau Canyon. Steep W, N, and E aspects above 10,500' should be considered most suspect, as these slopes accumulated early season snow, which has since turned into depth hoar and been buried by the season's entire snowpack.

  The best way to manage the risk from persistent slab avalanches is to make conservative terrain choices. Persistent slabs can be potentially triggered by a skier’s/boarder’s weight, even weeks after the last storm. The slabs often propagate in surprising and unpredictable ways, making this problem difficult to manage.

  

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Very Likely

  Size

  1–2

  Strong southwest winds have created wind slabs on leeward slopes and terrain features that are reactive. Winds are forecasted to continue for the next several days and will continue to redistribute the snow.

  On Sunday afternoon, a medium-sized soft slab avalanche was triggered during explosive mitigation work at the Snowbowl on a reactive northwest slope. These avalanches will be a significant risk over the next few days and could easily be triggered naturally or by a backcountry traveler.

  

• 

  Storm Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  1–2

  This storm began with soft, low-density snow. A density change occurred as the sun rose, and as a result, the top ~24" of the new snow is "upside down" and is more reactive. Recent warm weather on Thursday and Friday afternoons created a distinct sun crust on all but north-facing slopes at most elevations. This crust will provide a low friction bed surface and a poor bonding interface between the crust and new snow that falls upon it. These two factors will extend the time required for stabilization to occur.  Over the night, as of 6 am, 22 inches of snow has fallen at 10,800 feet across the last 24 hours, with an additional 3-7 inches forecast during the day on Tuesday. The winds are expected to continue from the southwest with gusts of 40mph which continue to transport snow to leeward terrain features.