Eastside Region

Avalanche problems

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  1–2

  Over a foot of new snow fell overnight and this was accompanied by moderate to strong winds out of the southwest. While winds are expected to drop in speed today you should expect large and sensitive wind slabs on leeward slopes near and above treeline. Be particularly cautious if wind speeds are stronger than expected.  It is imperative to remember that even a small wind slab avalanche today might be enough to trigger a much larger and more destructive Persistent slab avalanche.  Be suspect of terrain features that encourage drifting such as the leeward sides of ridgelines, gully features, and cross-loaded depressions. Blowing snow, recent cornice growth, stiff hollow feeling upside-down snow, and a textured, uneven snow surface are all signs of recent wind transport. Use these signs to identify and avoid slopes with recent wind deposits. 

• 

  Storm Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  1–2

  Storm instabilities such as Storm slab avalanches and loose surface sluffs will be likely today at all elevations.  Be wary of steep unsupported terrain features and remember that even a relatively small storm slab avalanche has the potential to step down to weak layers deeper in the snowpack resulting in a much larger persistent slab avalanche. Convex rollovers and slopes over 30° in steepness are particularly suspect today. When in doubt, avoid being on or under avalanche terrain and be cognizant of your exposure to terrain features that increase the consequences of avalanches. This includes road cuts, gully features, cliff bands, and mid-slope depressions. Be wary of overhead hazards today and avoid being in or underneath avalanche terrain.

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–3

  A significant new load was added to our snowpack overnight in the form of fresh snow and importantly over 1” of Water Equivalent.   Field observations continue to highlight our weak structure, and this rapid loading event has brought back concern over the potential for large persistent slab avalanches. This is not our typical Sierra snowpack and Forecaster confidence is low when it comes to the likelihood and sensitivity of this problem, however, if an avalanche is triggered on these deeper weak layers is today it is likely to be very large potentially running near the ground.  The weight of a skier or a wind slab or storm slab avalanche might be all that is needed to tip the scales and trigger a large destructive avalanche.   Persistent Slab problems challenge our patience and managing this problem requires extensive evaluation and deliberate terrain choice.  Northerly and Easterly facing terrain that still held snow from November and December are our potential problem areas particularly in the northern half of the range.  Don’t be afraid to investigate the lower reaches of the snowpack to see if old snow is present in the areas you wish to travel. This may mean digging all the way to the ground if you suspect old snow is present. Remember that persistent slab avalanches often propagate across and beyond terrain features that would otherwise confine surface instabilities such as wind or storm slab and in some cases persistent slab avalanches can be remotely triggered from adjacent slopes. Give yourself a wide safety margin, be wary of hazards that may reside above you, and use terrain choice to limit your exposure.