Salt River and Wyoming Ranges

Avalanche problems

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–1.5

  Yesterday, 6-10" of snow fell in this zone, accompanied by strong winds that build fresh slabs. Continued winds blowing out of the NW last night helped these slabs to grow in thickness and distribution. This snow fell on a variety of surfaces, including old, hard wind slabs and icy crusts on slopes that face the sun. These stiff surfaces mean that any slide you do encounter will pick up speed quickly as it runs downslope. This problem will be most common in alpine terrain and at upper elevations where it remains possible to trigger slides on slopes over about 35 degrees in steepness. The slabs could be more sensitive to triggering where they overlie hard, wind-polished surfaces or crusts. If you see cracks shooting out from your skis or sled, consider where even a small avalanche could carry you before riding that really steep slope.  In the alpine terrain of the Tetons, spindrift trickling down cliffs and cross-loaded into narrow terrain features often forms slabs, as well as on the aprons below. Avoid steep slopes where you find these indications of recent wind loading. 

  ADDITIONAL DISCUSSION

  In areas that are not affected by the wind, yesterday's snow poses a different potential hazard. The forecast is calling for cold temperatures but clear skies. As we transition to spring, the sun continues to move higher in the sky and increase its input to the snow. I'd expect to see small, natural loose snow avalanches running in steep, rocky terrain. These sluffs will also be easy to trigger if you're riding in steep terrain, particularly where stiff surfaces exist. This type of instability can be particularly pronounced in the very steep and rocky couloirs that are common to certain areas of this zone. 

  This problem will be more prominent in southern portions of the zone that received greater snowfall amounts. 

  

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Unlikely

  Size

  1.5–2.5

  Two days ago at Cliff Creek on a northerly aspect, I found a shallow snowpack under a meter in depth composed primarily of weak, faceted snow. This is reflective of some areas of the zone that have remained shallow. Yesterday's snowfall was likely not substantial enough to change conditions at many middle and lower-elevation spots, but broadly, a mixed bag of conditions still exists. Triggering a 2-4 foot thick persistent slab avalanche on weak snow deeper in the snowpack is unlikely, but not impossible. You'll do well to keep them in mind and continue to factor them into your decision-making. It would take a dose of very bad luck, but you could trigger a large avalanche in very steep (over 35 degrees), alpine terrain that is more likely to have thin spots where your weight may reach the weak layers.  The weak layers we've struggled with most of the winter have not gone away, but they've become less reactive to the weight of a skier or rider over time. Due to their depth in certain areas, they've also become very difficult to impact with your weight. 

  Triggering a persistent slab avalanche is unlikely, but could be found in terrain with the following characteristics:

  • Steep and Southerly: slopes in prime-time avalanche terrain around 35-45 degrees ranging E-S-W on the compass.
  • Wind-affected: heavily wind-loaded by past or recent wind events.
  • Alpine flavor: complex, windswept terrain with rock ribs, cliff bands, or convexities.

  Deep Persistent Slab: In addition to the persistent slab problem type, weak snow near the ground persists, primarily on the southern half of the compass in the middle and upper elevations. This layer is considered dormant at this time with the last activity observed on January 16th.