Continental

Avalanche problems

• 

  Storm Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  1–2.5

  Recent pulses of light to moderate snowfall have created several distinct storm snow interfaces, and those layers proved sensitive on 4/18. A couple of skier- and machine-triggered avalanches were observed on both solar and shaded aspects. Today, another 4–6+ inches of snow is expected above 3000', adding stress to an already reactive upper snowpack. This additional load may also increase the chance of avalanches stepping down into weak snow buried deeper in the pack.

  The main concern today is storm slab activity. Increasing winds should build deeper and more sensitive slabs near ridgelines and in wind-channeled terrain, where snowfall and drifting will be most pronounced.

  Below 3000', warmer temperatures have limited snowfall accumulation, but wet loose avalanches will still be possible on solar aspects.

  

• 

  Loose Wet

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–2

  Wet loose activity was very active on 4/18, when new snow quickly became reactive on solar aspects. Cloud cover should help limit natural avalanche activity today, but it has also prevented a strong overnight refreeze. As a result, human-triggered wet loose avalanches will remain possible on solar aspects at all elevations. At lower elevations, the snowpack has become isothermal, and steep solar terrain below 3000' should be avoided.

  Wet loose avalanches become more likely as surface snow becomes wetter and that wetness penetrates deeper into the snowpack. Once 4–6 inches of the surface snow is wet, loose avalanches are possible. On bigger slopes, more snow can be entrained, producing a larger avalanche.

  Avoid traveling on or below steep slopes or terrain traps where more than 4–6 inches of wet snow exists.

  

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  2–3

  Persistent Slab: Triggering a persistent slab avalanche is becoming increasingly likely.  Multiple weak layers remain a concern within the snowpack. These layers are being progressively loaded by new snow above 3000' and may become reactive as snowfall continues to accumulate. Our area has remained fairly dry over the last two months, allowing weak snow to adjust to the slab above. Even so, any increase in load or rapid warming has led to increased sensitivity. This was last observed on 4/9, when 4–8 inches of new snow combined with sunny skies produced multiple human-triggered avalanches, both direct and remote, as well as hundreds of large natural wet loose avalanches.

  Additional snowfall today and through the next week will continue to stress these weak layers.  The stress vs strength relationship is continuing to evolve with the stress side of the scale becoming heavier.  The best way to reduce risk is to choose simple terrain today. If you choose to travel in avalanche terrain, only expose one person to a slope at a time, keep eyes on your partners, and identify safe spots before committing to terrain. Keep in mind that if avalanches fail on older weak layers, slabs may propagate wider and run farther than expected.

  Deep Persistent Slab: Buried weak snow near the ground has remained unreactive for quite a while. Triggering a layer this deep is currently unlikely, but as spring thaw progresses this layer may become stressed enough to produce large avalanches. Keep this on your radar as conditions continue to change later in the season.