Central Sierra Nevada

Avalanche problems

• 

  Loose Wet

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  2

  The strong March sunshine and very warm daytime temperatures will cause wet snow to form sun exposed aspects today. These aspects have not been through enough melt freeze cycles for good drainage channels to form through the recent snow or for the recent snow to transition to corn snow. Loose wet snow avalanches will become possible today as wet snow forms in response to daytime warming. Most of these loose wet instabilities should manifest as small roller balls, pinwheels, and point releases, but some of them could entrain enough snow to cause problems for backcountry travelers. 

  Sinking into boot-top deep wet snow and smaller surface wet snow instabilities like roller balls and pinwheels indicate that enough wet snow exists for problematic loose wet avalanches. These signs indicate that the time has come to move to more frozen slopes, move to less steep slopes, and/or switch activities for the afternoon. 

• 

  Glide Cracks

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  3

  Large overhanging cornices formed above many wind loaded slopes along exposed ridgelines during the recent storm. Some of these cornices failed during the storm, and some have broken under the weight of a person or snowmobile since the storm, but many of them still remain perched above wind loaded slopes. Today's warming will weaken these cornices, and they may become easier to break. These cornices could fail well away from their edges and would result in large heavy pieces of dense snow hitting the slopes below them. These large blocks tumbling down a steep slope could easily injure a person. If these cornices do break, they will provide very large triggers for the wind loaded slopes below them and could cause wind slab avalanches on those slopes even though human triggered wind slab avalanches have become unlikely. This wind slab cornice combination would be especially suspect in complex or extreme terrain like couliors or unsupported wind loaded slopes where less well bonded wind slabs may still lurk.  

  Identify where cornices exist and stay well back from their edges. Often determining how much a cornice overhangs a slope is difficult, and even when the overhang is visible, they can break behind that point. Giving these large cornices more space than seems necessary represents a wise choice.