Mount Shasta

Avalanche problems

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Unlikely

  Size

  2–2.5

  While unlikely, there remains a potential for large avalanches on buried graupel layers. This is a low likelihood, high-consequence scenario.

  These graupel layers are widespread in the upper snowpack and have been found on the west and east sides of the forecast area at all elevations. Feedback on these layers has been limited in snowpack tests, but they are suspected in two large natural avalanches, including the slide observed Wednesday in the Old Ski Bowl. Both avalanches released during significant storms, which rapidly loaded the snowpack. The February 14th graupel layer is buried about three feet deep near treeline on Mount Shasta and sits atop a melt-freeze crust. Any avalanche failing on a buried graupel layer would propagate widely and be difficult to escape. 

  We don't often experience persistent instabilities in the forecast area. Here are some considerations to help manage this current problem while additional information is gathered on the sensitivity of these layers:

  • Today's warm temperatures will continue to send meltwater through the snowpack. While very challenging to predict, the potential exists for meltwater to pool and weaken these weak layers to the point of failure. Steep, warm slopes in areas where the graupel layers have been identified - such as Power Bowl and Sun Bowl - deserve extra caution.
  • Consider avoiding steep terrain below cliff bands. These are locations where graupel may have accumulated.
  • Persistent slabs are often triggered in areas where the weak layer is closer to the snow surface and more easily affected by the weight of a skier or rider. These include areas with shallower snow depths or thin spots in the snowpack, such as near rocks.
  • Signs of instability - like shooting cracks or collapses - can be limited and spatially variable. You may not observe any signs of instability before triggering an avalanche. 
  • Multiple ski or sled tracks on a slope do not prove that it is "safe". 
  • As always, evaluate the consequences before committing to steep terrain. Or, make conservative terrain choices and give the snowpack more time to adjust to the recent load and warming. 

  

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–2

  It is possible to trigger a large avalanche in wind-drifted snow at upper elevations. Tuesday's storm dropped about 12 inches of wet, dense snow (3.28" SWE) at the Old Ski Bowl (7,600 feet). Higher elevations probably received over two feet of drier snow. Winds have blown predominantly out of the west/northwest over the past three days. Today, northwest winds continue with dry snow available for transport above ~9,000 feet. 

  You are most likely to encounter the problem on steep slopes (>35 degrees) on the leeward side of prominent ridgelines. Watch for blowing snow, fresh cornices, and pillow-shaped features to alert you to recently wind-drifted areas, and consider avoiding these slopes. Shooting cracks are a clear sign of unstable snow. Stick to wind-scoured or sheltered terrain to help manage this problem.

  

• 

  Loose Wet

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–1.5

  Numerous small (D1-1.5) wet loose avalanches have been observed in recent days. A poor overnight refreeze and warm temperatures today may cause more wet loose instabilities on steep (>35 degrees), solar aspects, especially under rocky terrain features. You may also find this problem at warmer, lower elevations on the north half of the compass. 

  Even small wet loose slides can carry you into undesirable terrain like cliffs and gullies. If you observe signs that the snow surface is losing cohesion, such as fresh rollerballs, move to mellower or shadier slopes.