Banner Summit

Lawinenprobleme

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Possible

  Größe

  2

  Triggering a large, 18-30" thick avalanche is most likely on slopes where you check all of the following boxes:

  • Steep: Slopes steeper than about 35 degrees.
  • The weak layer: Well-developed facets exist in the middle of the snowpack on the vast majority of slopes. Assume this weak layer exists until you do not see it in your snowpit or sled trench.
  • The slab: Where wind has stiffened the snow in the upper part of the snowpack and/or formed hard drifts on the surface. 
  • Aspect: The recent avalanche activity has been focused on roughly two-thirds of the compass: W/NW-NW-N-NE-E-SE. Most south and southwest aspects do not appear to have the thick layer of well-developed faceted snow in the middle of the snowpack.

  On slopes where you don't check all the boxes, triggering slab avalanches is less likely. 

  The snowpack has had some time to "catch its breath" in recent days, decreasing the chances of triggering large slides. However, this wretched-looking snowpack needs way more than a few days of R&R to cure its ills. Some other information to keep in mind when you're planning today's adventures: 

  • Because the weak layer is more deeply buried around Banner Summit, it's getting more difficult to trigger avalanches. The tradeoff: unstable slopes may not give you obvious "red-flags" like snowpack collapsing, shooting cracks, or poor stability test scores. Also, any slides you trigger will be around 2 feet thick. 
  • There's a real chance of remotely triggering slides: triggering them from your location in gentler terrain above, below, or to the sides of steep slopes. Be aware of the terrain you are in and the terrain above you.

  We may begin loading the snowpack (snowfall and wind) again this afternoon and will load it tonight. With the impressive layer of crumbly, faceted snow that exists on most slopes, even a little snowfall or wind-blown snow can tip the stability scales in the wrong direction. If the storm arrives early and you're still out playing, reevaluate your travel plans to get home safely. 

  ADDITIONAL DISCUSSION - WIND SLABSIn the past few days, wind formed thin drifts and slabs near exposed ridgelines. Today's increasing winds and light snow showers could do more of the same. Though small in size, the slabs may be touchy on all aspects and will be adding stress to the weak snow described above. Any small slides you trigger have the potential to "step-down", creating a much larger and more dangerous avalanche.