Salt Lake

Avalanche problems

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Very Likely

  Size

  4

  The situation is very simple - there is a persistent weak layer (PWL) of old, faceted snow near the ground with 3-10 feet of snow on top of it. This layer has been fracturing and producing large and destructive avalanches over the past week. This morning we are adding two huge stressors to this fragile snowpack in the form of heavy wet snowfall and elevated winds. We can't know if this will be the tipping point that will cause the snowpack to become unglued, but we do know that the avalanche danger and likelihood of avalanches will be on the rise again.

  This layer exists on west, north, and east-facing slopes where old snow lingered and weakened in November and was buried by December snowfall. It doesn't exist on south-facing slopes because it melted away in November, and December snowfall landed on bare ground on those slopes. The most likely places to trigger a slide in that persistent weak layer are slopes with some wind-loading especially on more northerly facing slopes with the weakest snow.

  Today, human-triggered avalanches will become very likely, these avalanches can be large enough to catch, carry, bury, and kill a person. Given the new snowfall, elevated winds, and poor snowpack structure I would avoid any terrain steeper than 30 degrees, with any steep terrain above or attached to it. Today is not the day to push it.

• 

  Storm Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  2

  With warm, wet snow on the way - new snow avalanches will become possible on all aspects and elevations and will likely get bigger and more active over the next few days. Extreme caution is required. Today we should be getting 12-18" of new snow, and up to 34" of snow by the time this is all said and done. While snow totals are important, what we truly pay attention to is what RATE that snowfalls and how quickly it loads the snowpack. We call this precipitation intensity, and if those rates stay elevated or increase throughout the morning we could see the avalanche danger spike and more new snow avalanches occurring. Keep an eye on the sky, if the snow rate rapidly increases you know the danger is on the rise.

  During these times of high precipitation intensity, both fast-running sluffs and soft slab avalanches will be possible. These human-triggered or natural soft slab avalanches may even step into the old-faceted snow producing significantly larger avalanches.

  With such warm temperatures, there could be periods over the next few days that we may get rain on snow at lower elevations. Know that rain on snow is always a red flag and danger will spike in those areas. If you are getting rained on, it might be a good sign to go seek other terrain options.

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  3

  The winds have been cranking now for multiple days. These strong winds in combination with a few inches of new snow will have drifted snow and formed fresh slabs. The issue with yesterday's freshly formed wind slabs is they will likely be hidden under a few inches of new snow from this morning and will be harder to identify.

  Know that slabs of wind drifted snow will exist on mid and upper elevation terrain features that snow could be deposited, such as ridgelines and gullies.

  This afternoon's elevated winds in combination with new snow will continue to form both soft and hard slab avalanches in mid and upper elevation wind drifted terrain. As the winds continue to blow, these slabs will become more firm and cohesive. This can allow you to travel out farther onto the slope before it breaks, and can fail larger and wider than expected. High winds can deposit snow on all aspects but give west through north through east extra caution, as triggering an avalanche that initially fails in the wind-drifted snow will likely break down more deeply into the weak faceted snow below.