Provo

Avalanche problems

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  3

  Steep, rocky terrain should still be avoided in the mid to upper elevations on northwest to east facing slopes. The additional wind loading will add stress to the poor structure and it is possible that skiers, snowmobiles, and cornice-fall, etc, in the right spot may trigger a devastating avalanche. Danger Trend: Steady to Increasing Currently, there is a very strong slab of snow sitting on top of weaker (faceted) snow at the base of the snowpack. When it comes to avalanches we need two things: Initiation and propagation. While the extended column test (ECT) remains the bread and butter test for the backcountry travelers we are now starting to see ECT scores that show no results (no propagation) across the buried weak layer. The ECT test is one of the best tests to perform on the snowpack as it shows both initiation and propagation while performing the test. However, it has one weakness, when the slab becomes very strong it can be very hard to initiate the weak layer by hitting the top of the shovel blade. Just as we are riding across the snow surface it's hard for our weight to effect the weak layer.

  Initiation or triggers can come in many forms: Loading (adding weight) by wind or snow, skiers, snowboarders, cornices, explosive, to name a few.

  The Propagation Saw Test (PST) only tests propagation of the weak layer (no initiation). In the video below you can see the weak layer propagate up the column followed by the slab of snow crashing down. What does all this mean? well, if you are unlucky enough to initiate or trigger the avalanche it's clear to me that you can still propagate a crack through the weak layer and cause a very large and deadly avalanche. The probability is low, but the consequence is high.

  Video: Propagation Saw Test - showing the weak layer and slab.

  When will this layer go away?

  Info about this layer and where it exists

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  2

  The southwest winds have and will continue to scour and erode any available snow and deposit it in the form of soft and hard wind drifts in the mid and upper elevations, even in odd and unusual locations. Yesterday, we had two people trigger hard wind slab avalanches at the upper elevations. We also had one skier trigger a hard wind slab, taking a ride in the avalanche. This should be a hint that these drifts are not to be messed with.

  In some areas, these drifts may land on weak snow surfaces formed over the past week and may be surprisingly sensitive and possibly triggered from a distance. These areas are more likely found in the sun and wind sheltered terrain where the snow surfaces are susceptible to decay. Wind drifts are often smooth, scalloped, and rounded . Soft wind slabs you're "in the snow" with your sled or skis; hard wind slabs you're "on top of the snow". Hard slabs are often trickier because they allow you to get well on to them before they collapse. For today, continue to look for and avoid rounded, pillowy, or hollow sounding snow.

  * Any wind slab avalanche triggered does have the potential to pull out a much larger avalanche in areas that have a persistent weak layer present.