Maritime

Lawinenprobleme

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  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Possible

  Größe

  1–2

  The most likely avalanche problem for a person to encounter today will be wind slabs that formed due to strong southerly winds.  Moderate to strong southerly winds were observed yesterday near Thompson Pass from road level up to high elevation ridges.  These winds were actively forming wind slabs that are expected to be possible for a person to trigger today in specific areas such as cross loaded terrain and the lee side of high elevation ridges and terrain features.  Wind speeds were forecasted to increase along high elevation ridges last night with gusts to 60 mph possible.  With 12-18" of settled storm snow from last weekend expect to find wind slabs up to 2 1/2 feet in depth above 2000'.  Below 2000' a rain crust exists which will limit snow available for transport to a few inches.  

  Terrain that is in close proximity to the Thompson Pass gap will be the most likely area to encounter fresh wind slabs.  As you move South or North from the pass the wind's effect will be less, however, lee slopes just below high elevation ridges are expected to be affected throughout our forecast zone.

  Generally, wind slabs are fairly easy to identify visually and by feel.  Today, they will be more difficult as our area is expecting 6-12 inches of new snow in the next 24 hours, which will mask where these slabs exist.  Winds are forecasted to be lighter but will be blowing in the same direction, which will point you toward where these slabs formed yesterday.  Try to anticipate where these wind slabs exist and avoid areas where they are most likely to be an issue, such as cross-loaded gullies and lee convex terrain.

   

   

  

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  Storm Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Possible

  Größe

  1–1.5

  Small storm slabs are expected to begin to form today.  The major issue with the new snow is that it will hide previous wind slab formation near Thompson Pass and also add weight to these slabs that could be sensitive in specific areas.  Shallow new snow instabilities are possible in steep terrain that was previously unaffected by wind, however these are expected to be small and consequences will be determined by the terrain.

  The hazard for this problem will be increasing by tomorrow as snowfall is expected to continue coinciding with rising temperatures.  Expect this problem to jump to the #1 slot at some point in the next 24 hours as wind slabs decrease in sensitivity as they age and storm slabs grow in depth.

  

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  Deep Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Unlikely

  Größe

  2.5–3.5

  Our snowpack has undergone a major change since the beginning of January.  What began the month as a fairly thin snowpack with very thick vegetation below brushline has trasformed to a thick midwinter snowpack with the alders being mostly buried above 2000'.  Below 2000' the snowpack remains thin.

  This transition is a very welcome sight but it has put significant stress on our snowpack, especially during times of heavy precipitation.  On the 11-12th we received 100" of snow on Thompson Pass in a 48 hour period.  This caused a significant natural avalanche cycle that failed at weak layers in the mid snowpack.  As the new snow was allowed to settle  a much stronger snowpack was observed the following week.  Again on the 19th we received a significant snowfall event with 30" on Thompson Pass in 24 hours.  This produced a few large avalanches (see avalanche tab below bottom line) but was much less significant than the previous cycle.  

  This Natural avalanche pattern along with recent snowpack observations point to the likelihood of triggering a deep slab avalanche being low, but is possible still with a large load or  in steep rocky terrain where storm slabs are thinner.  Large loads would include heavy snowfall events and the days directly proceeding them, cornice fall and large groups.