Ogden

Problèmes avalancheux

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpin
  • Limite forestière
  • Sous la limite forestière

  Probabilité

  Likely

  Taille

  3

  The situation is very simple - there is a persistent weak layer (PWL) of old, faceted snow near the ground with 3-4 feet of snow on top of it that can avalanche. Winds increased from the south and have likely been loading the slopes where this PWL exists.

  This layer exists on north, and east-facing slopes where old snow lingered and weakened in November and was buried by December snowfall. This layer seems to be fairly widespread at upper elevations above 8,500 feet and more spotty at mid elevations. It doesn't exist on south and west facing slopes because it melted away in November, and December snowfall landed on bare ground on those slopes.

  Since Christmas Eve, snowfall containing up to 6 inches of water has been added to the snowpack. We focus on water amounts because that tells us how much weight is added to the snowpack. For a slope the size of a football field, snow with 6 inches of water weighs 2,100,000 pounds. Imagine that amount of snow crashing downhill.

  How will we know when this avalanche problem heals? That's a tough question to answer, and we mainly have to let the snowpack answer it. For now, avalanches are still happening and that's all I need to know. As we look into the future, it will heal, but I can't tell you when. We will be monitoring the snowpack and avalanche activity and keep you updated.

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpin
  • Limite forestière
  • Sous la limite forestière

  Probabilité

  Possible

  Taille

  2

  This morning, south winds increased some and have likely been forming fresh slabs of wind drifted snow. Even at 7700 feet, winds have increased. Yesterday, a regular observer near Ben Lomond Peak observed increased west winds moving snow at mid elevation ridgelines (see video below). These fresh wind slabs weren't reactive yesterday, but may be today.

  For the snowpack, when the winds drift snow, it's the same as if snow is falling out of the sky. The snowpack doesn't care where the snow comes from, it feels the added weight. So, on northerly facing slopes, these winds have added snow and weight and stress to the avalanche problem listed above.

  While these winds have mostly formed drifts on northerly facing slopes, they can load any slope because winds swirl and change direction as they pass through the mountains. What to do? Avoid any steep west, north, or east facing terrain that has avalanche problem listed above. If riding south facing avalanche terrain, look for evidence of fresh drifts and wind slabs that look wavy, rounded, smooth, and pillowly and avoid them as well. Fortunatley, those fresh drifts are easy to see and go around.

  (video - B. Brandt)