Salt River and Wyoming Ranges

Avalanche problems

• 

  Wet Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  1–2

  After several warm days and cool nights, water appears to be reaching weak layers and crusts in the upper snowpack. Two avalanches were triggered yesterday afternoon in the nearby Teton forecast zone, one remotely by a forecaster south of Teton Pass in a sunny, wind protected bowl and one triggered by a snowcat pushing snow onto a sun-baked slope at JHMR (see photo).

  Recent avalanche activity prior to these two slides was limited to wet loose sluffs, a few of which were large and potentially dangerous. Those occurred primarily on the first warm days last week (Thursday and Friday) when sun heated up fresh snow. Since that time, every day seemed to be a replay of the previous one, with sunlit surfaces becoming wet 3-4" down but no reported wet sluffs or slabs. Rcent snowpits are showing water pooling on crusts at various depths beneath layers of dry snow. Assessing the exact location and depth of these crusts prior to riding on a slope isn't really feasible due to the spatial variability of the layers, but observing the warm temps, calm wind, and slush on the surface is easy. Monitor the snow surface as the day heats up. Think twice if you are sinking in past your ankles and be mindful of potentially forceful wet loose avalanches even on less sunbaked slopes.

  

• 

  Deep Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Unlikely

  Size

  2–3

  Weak snow that formed in December persists at the base of the snowpack across the entire Greys River forecast zone. However, the thickness of the hard slabs that overlay this weak snow varies based on geographic location. In the middle and upper elevations of the Salt, Snake River, and deeper portions of the Wyoming Range, these weak layers are buried 3-5+ feet deep making it difficult for a human to impact them. In shallow parts of the forecast zone, such as the far eastern side of the Wyoming Range, these slabs are only 2-3 feet thick making it possible for humans to trigger avalanches on the buried weak layers. Shallow, rocky, and unsupported terrain on the north half of the compass is where this problem has been most active. Keep in mind that a large trigger such as a cornice fall could trigger one of these very large avalanches, even in areas where the snowpack is deep.

  Careful snowpack evaluation is required in the Greys River zone due to variable snow depths. Probing or digging can provide useful information about the depth to the weak layers preserved at the bottom of the snowpack. This evaluation is critical if you are riding in a shallow part of the zone. A total snow depth less than 6 feet (200cm) is a red flag.

  The last reported human triggered avalanche involving deeply buried weak layers occurred on March 9th on the far eastern side of the Wyoming Range.