Bulletin d’avalanche

Problèmes avalancheux

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpin
  • Limite forestière
  • Sous la limite forestière

  Probabilité

  Possible

  Taille

  1–1.5

  Yesterday (Monday), the PAC toured into the northwest portion of our advisory area. Around mid-day, winds increased out of the SW/W. Winds were drifting and blowing snow (especially near ridgelines) and forming sensitive wind slabs on E/NE aspects (photo to the right). There is still snow available for transport, despite the warm weather over the weekend. Winds have been steadily shifting from SW to NW and are forecasted to keep moving clockwise around the compass to N/NE tonight. You're most likely to encounter a wind slab on slopes above 7000 feet, particularly on north and east-facing aspects. These wind slabs have likely formed on a variety of very firm surfaces, mainly a melt-freeze crust. Sensitive slabs atop a firm crust is a recipe for an avalanche, the only missing ingredient is a trigger.

  Local terrain features can influence upper level winds and wind direction can vary by zone. This leads to a level of uncertainty with where exactly wind slabs could be lurking. All wind-exposed slopes should be carefully evaluated for the presence of wind slabs. Pay attention to clues like shooting cracks from your skis or machine. If you feel a dense or hollow feeling in wind-exposed terrain, you've found evidence of a wind slab. Find aspects that are not presenting these clues to avoid wind slab avalanches.

  

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpin
  • Limite forestière
  • Sous la limite forestière

  Probabilité

  Unlikely

  Taille

  1–2

  Last week, we had multiple reports of snowmobile-triggered avalanches (near Council Mtn.). One in which a snowmobiler was caught, able to ride out to the side, but injured (near Box Lake). These avalanches were failing on buried weak layers from January. On average, they ranged from 1-3 feet deep, were in medium to small pockets, and were large enough to bury, injure, or a kill a person. All avalanches were on either NE or E aspects between 7200 and 7500 feet and were in protected pockets of wind-sheltered terrain. 

  Although becoming unlikely to trigger, a persistent slab avalanche cannot be completely ruled out. The weight of a person is very unlikely to impact these buried weak layers. Snowmachines are more likely to find and impact these buried weak layers. Buried weak layers, particularly surface hoar, are spotty and can be difficult to find. The only way to completely avoid a persistent slab avalanche right now is to avoid slopes between 7-7500 feet that face NW, N, NE, or E.