Seward and Lost Lake

Avalanche problems

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  2–3

  We are still concerned with the potential of triggering a large avalanche on a weak layer of surface hoar buried 1 to 3' deep. This has been responsible for over 20 human-triggered avalanches since it was buried in mid-February. The last known avalanche on this weak layer was 12 days ago, which resulted in a fatality. The limited avalanche activity most recently is likely a combined result of people avoiding the problem, and the layer slowly becoming more difficult to trigger. But the problem has not gone away. 

  The surface crusts that have been forming and making this layer more difficult to trigger will not be present today. This will increase the likelihood of triggering a large avalanche. Eventually the melt/freeze cycle may make this problem go away, but in most places where this layer exists the melt/freeze layer has not made it deep enough into the snowpack to impact this weak layer. This is a dangerous problem that has been difficult to predict since it got buried. We've seen its destructive potential, and we're still recommending to avoid traveling on or below steep terrain to avoid the problem.

• 

  Loose Wet

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  2–3

  Recent Avalanches: We have seen a very active week of wet snow avalanches, with several large glide avalanches running into valley bottoms. There were large wet slab avalanches in the Girdwood valley and in the Carter Lake area yesterday, and we continue to see wet loose activity on steep solar aspects. There are currently two large glide cracks on Mt. Marathon that threaten popular hiking areas below, and last week one large wet snow avalanche ran down into Lowell Canyon.

  With a warm and cloudy night last night, warm temperatures and a chance for some sunny skies this afternoon, we should expect to see continued wet snow avalanche activity today. This includes wet slabs, wet loose, and glide avalanches. We have already seen a very active week of wet snow avalanches across all of our forecast zones, and conditions today will likely continue that pattern. Some of these avalanches have been running well into low-angle, low-elevation runout zones.

  Avalanche activity will become more likely as temperatures rise through the day. Last night's warm and cloudy weather will mean that we saw little or no refreeze overnight. This means we will likely see the onset of natural activity earlier today than we have seen over the past few days, and it will increase the chances of seeing more large wet slab avalanches like we saw yesterday. There may still be dry snow on northerly aspects at upper elevations, but that is also prime habitat for the weak layer of buried surface hoar (more on this in Problem 2 below). Conditions are complicated and dangerous right now. The best way to manage these problems will be to avoid traveling on or below steep terrain.

  Cornices are also failing in the heat of the day. This can often trigger larger avalanches on slopes below. These can occur without warning, so it is important to avoid spending time under large cornices.

  Wind Slabs: Easterly winds will continue to increase through the day, building a new round of reactive wind slabs. This will likely remain small because there is limited soft snow on the ground available for wind transport, but the wind always finds a way to move some snow. Watch for unstable conditions at upper elevations, especially below ridgelines, convex rolls, and loaded gullies.