Flathead Range & Glacier NP

Avalanche problems

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1.5–3

  This past week's heavy snowfall has added a significant load, stressing the snowpack on slopes harboring the buried surface hoar. The widespread layer responsible for multiple avalanches since late-January continues to propagate in snowpit tests, remains a concern, and dictates our travel plan on slopes facing NW-NE-S.

  Due to the depth of the weak layer, you are unlikely to notice signs of instability, such as collapsing, before triggering an avalanche. Locations where your weight may impact this layer are where the snowpack is variable and thin, such as wind-swept slopes, those peppered with rocks, or locations that missed out on the recent snowfall.

  The only sure way to minimize your exposure to this problem is by avoiding it. Continue to choose low-angle slopes not connected to overhead avalanche terrain.

   

   

   

  

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1.5–2.5

  Two generations of wind slabs are present throughout the forecast area.

  During this past week's stormy weather, gale force southwesterly winds built thick drifts on NW-NE-SE slopes below ridgelines, saddles, and mid-slope ribs. These are older and likely less reactive, but fresh snowfall following the wind event has helped disguise them. Triggering an avalanche in this terrain can result in a much larger slide described in the Persistent Slab problem above.

  Beginning Friday, light to moderate north and east winds redistributed snow onto atypical slopes at all elevations. These are more recently formed and easier to identify. Winds from this direction often leave slabs in unusual locations.

  Look for tell-tale signs that the wind has been at work: an etched or scalloped surface, dunes or pillows, and fresh cornice growth. Cracking in the surface snow indicates you have found a slab, while shooting cracks are the sign of a sensitive slab.

  Choose terrain unaffected by these winds to avoid this problem and maximize your enjoyment of the great snow conditions. 

   

  

• 

  Loose Dry

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  1–2

  Substantial loose dry snow blankets the hillsides throughout the area. On steep slopes, riders should expect to trigger sluffs in the cohesionless snow. If the sun comes out for an extended appearance, expect a natural loose snow avalanche cycle on southerly aspects. We expect both dry and wet loose avalanches to occur today.

  In some locations, this snow rests on a crust, which inhibits bonding and allows loose snow avalanches to travel farther than expected. With plenty of snow available for entrainment, slides could become sizeable.

  Limit your time spent in long-running gullies where escape can be difficult or above terrain traps where debris can pile up surprisingly deep. 

  Snow bombs falling from trees, water dripping from trees and rocks, and rollerballs are all signs that the surface snow is warming and may be a precursor to a wet loose slide. Be aware that rocky slopes above you may be warming faster than the terrain you are on, potentially sending debris to your location.