Continental

Problèmes avalancheux

• 

  Loose Wet

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpin
  • Limite forestière
  • Sous la limite forestière

  Probabilité

  Likely

  Taille

  1–3

  Temperatures have warmed dramatically after this weekend's storm that deposited 2 feet on Thompson Pass.  Wet loose activity has been widespread on all aspects below 2000'.  Above 2000' wet loose activity has been occurring on all but northerly aspects.  Over the last 24-48 hours there have been multiple reports of wet loose slides stepping down and producing destructive wet slab avalanches in the D2-D3 range.

  Expect this activity to continue today although the mass and frequency of natural activity are expected to be lower as the previous 48 hours have removed a lot of snow already.  Avoid steep sunny aspects during the heat of the day especially when they end in a terrain trap.  Wet loose activity is an easy problem to avoid because it gives clear feedback and is very aspect dependent.  East aspects will be the first to warm and produce hazard.  The hazard will move clockwise around the compass following the sun with west/northwest being the last aspect of the day to warm up.  Keep in mind that slopes that are perpendicular to the sun will be the most sensitive.  Once more than 3-4 inches of the surface snow becomes moist, then wet loose activity will begin to occur.  Steep rocky terrain will be the first to be reactive.  The potential size of wet loose activity will directly correlate to the vertical relief and steepness of a slope.  

   

   

   

  

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpin
  • Limite forestière
  • Sous la limite forestière

  Probabilité

  Possible

  Taille

  2–3

  After a couple of days without snowfall and 2 nights of below freezing temperatures overall stability has significantly improved at upper elevations.  There were lots of slope testers out there yesterday with only a handful of human triggered avalanches reported in the D1-1.5 range.  Stability will continue to slowly increase, however, we need to be aware that a persistent weak layer is now buried 2-3 feet deep.  At this point it is unclear as to how well preserved this layer remains (was it crushed? Did it Cycle? Or is it waiting for a trigger?).  

  The persistent weak layer mentioned above consists of surface hoar that was buried on 3/9.  This layer has been identified prior to this weekends storm in the Intermountain and Continental zones on the northerly half of the compass above 3000'.  Before the most recent storm, this layer was reactive to skiers and produced multiple D1 skier triggered avalanches.  These D1 avalanches will now possibly be D2's or even 3's as the mass above the weak layer has significantly increased.  This weak layer is just above the very hard wind damaged snow created in late February.  This wind damaged snow will act as an effective bed surface and may allow avalanches that are initiated to have very wide propagations.  

  This setup is dangerous as not only does it have the potential to produce dangerous avalanches but identifying this layer can be challenging even for experienced users.  Making things further challenging, signs of instability will likely not be present with this weak layer due to its depth.  The likelihood of triggering this layer has gone down but the consequences have significantly gone up.  Buried surface hoar is notorious for being spotty in its distribution meaning that good stability can be observed in one location and an adjacent slope may have unstable conditions.  As stated above this layer has been identified north of Thompson Pass on protected northerly slopes.  We can not yet rule out that this layer does not exist in other areas.  Snow pits are a good tool to tell you where not to ski or travel.  Don't assume that negative results in a stability test mean a slope is safe.  When seeking out wind sheltered north facing terrain, realize that these are also the areas where buried surface hoar may exist.