Central Sierra Nevada

Avalanche problems

• 

  Storm Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Very Likely

  Size

  1–2.5

  A powerful storm will bring multiple feet of snow to the higher elevations of our forecast region with rain up to elevations of around 7000' early this morning.  This storm will have multiple storm snow layers with periods of high intensity snowfall.  Fluctuations in temperatures and snow levels will also create heavier over lighter snow layering.  Wet loose avalanches could occur at lower elevations along with storm slabs with wet snow characteristics.  Multiple storm snow avalanche concerns will exist for today.

  New storm snow with gale force southwest winds will create wind slabs in near and above treeline areas on NW-N-NE-E-SE aspects.  These wind slabs will exist along ridges, in gully features, and on open slopes.  Large and fragile cornices will build out along ridges and could collapse during this storm.

  Widespread large surface hoar and near surface facets were observed throughout the forecast region prior to the beginning of this storm on NW-N-NE-E aspects at all elevations.  There is a high likelihood that this surface hoar is now buried under the new storm snow that started last night.  Buried surface hoar could cause wide propagating avalanches at the old snow/new snow interface.  These avalanches could potentially be remotely triggered and run long distances.  

  

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  2–3

  Old weak faceted snow continues to exist multiple feet down in the snowpack.  This large storm loading event is expected to reactivate these weak layers and cause large to very large persistent slab avalanches to occur.  Recent avalanche activity and signs of instability have mostly been focused on the eastern and southern portions of the forecast region, especially in the Carson Pass to Ebbetts Pass areas on NW-N-NE-E aspects above 8000'.  These areas of concern could expand into other locations where a previous shallow and weak snowpack exists.