Galena Summit & Eastern Mtns

Problemi valanghivi

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  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alta quota
  • Limite del bosco
  • Sotto il limite del bosco

  Probabilità

  Likely

  Dimensione

  1–2

  6-10" of snow (0.4-0.8" of SWE) fell in this zone in the last 24 hours. Wind speeds increased significantly overnight, blowing at moderate to strong speeds out of the S-SW. As I write this, large wind slabs are building (and potentially failing naturally) in terrain exposed to the wind. These slabs will be largest and thickest at upper elevations, but you'll also find wind slabs in exposed lower and middle elevation terrain. The foothills of the White Clouds, Boulders, and Pioneers are common places to see lower elevation slides. Be on the lookout for wind slabs from the valley bottom to the mountain tops and expect them to be easy to trigger. 

  Wind slabs are building on top of persistent weak layers in the snowpack (read Problem #2 below). Because of this, the wind slabs you encounter today may behave more like persistent slabs than "simple" wind slabs. Fresh slabs will be reactive to your weight and may produce avalanches that break wider and deeper than you might expect. Triggering these avalanches remotely (from a distance above, below, or to the sides of steeper slopes) is a real possibility. Avalanches that break down into these deeper weak layers can be very large.

  Evidence of wind-loading may be subtle or may have been masked by additional snow that fell after slabs formed. Be on the lookout for wind slabs near ridgelines and on the sides of mid-slope features like gullies and ribs. If the snow you are moving through becomes deeper or denser you are likely traveling on a wind slab. Cracks shooting out from your skis or sled and collapsing of the snowpack are both clear indications you've found an unstable slab. Wind slabs that fail can be effective triggers for the deeper weak layers described below.

  

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alta quota
  • Limite del bosco
  • Sotto il limite del bosco

  Probabilità

  Likely

  Dimensione

  1.5–2.5

  Layers of weak snow in the upper snowpack can produce 1-3' thick slab avalanches. Expect to find weak, sugary facets on shaded slopes and crust+facet sandwiches on slopes that face the sun. You're most likely to trigger a slide involving these layers in areas where the wind has built a slab on top. However, enough snow has fallen here that avalanches failing in apparently sheltered terrain are a very real possibility.

  Friday, riders in the Baker Creek drainage reported remotely triggering 6 avalanches. The largest of these broke over 1,000' wide. The same day, professionals in the Boulder Mountains reported several very large natural avalanches (photo at right/above and in Problem #2 below). These slides failed in wind-loaded terrain and almost certainly involved layers of weak snow in the upper snowpack.

  The nature of these layers changes from slope to slope, it's safe to assume that they exist on most all slopes. Persistent weak layers produce avalanches that fail in unpredictable ways. They can break significantly wider and deeper than you might expect, producing much larger avalanches. Avalanches failing on persistent weak layers can be triggered from gentle terrain above, below, or to the sides of steep slopes, a process known as remote triggering. Today I recommend you choose simple, conservative terrain to play in. Pay close attention to the terrain around you and above you, and spend some time contemplating the potential outcomes of being caught in an avalanche in the terrain you are in. Cliffs, trees, and terrain traps magnify the consequence of even small slides.

  ADDITIONAL DISCUSSION: Triggering a very large persistent slab avalanche on weak, sugary facets buried deep in the snowpack would take a dose of bad luck. However, this scenario cannot be ruled out in rocky, wind-swept areas with variable snowpack depths. This terrain is common in the upper reaches of the Pioneer, Boulder, and White Cloud Mountains.