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Avalanche Forecast

Archived

Jan 18th, 2021–Jan 20th, 2021

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

North Rockies.

The warm and stormy period is winding down with one last pulse Tuesday. Watch for wind stiffened storm slabs at upper elevations and avoid terrain traps & convex rolls in the trees, storm snow may be resting on buried surface hoar.

Confidence

Low - Uncertainty is due to the limited number of field observations. Uncertainty is due to extremely variable snowpack conditions reported through the region.

Weather Forecast

We should get one last pulse of warm storm Tuesday before entering a clearing trend that extends for the foreseeable future.

MONDAY NIGHT: Freezing level peaking out at about 1500 m, strong west/southwest wind, no significant precipitation expected.

TUESDAY: Broken cloud cover, freezing level steadily lowering to valley bottom throughout the day, strong west/southwest wind, 5 to 10 cm of snow possible.

WEDNESDAY: Scattered cloud cover, freezing level at valley bottom, moderate to strong northwest wind, trace of snow possible.

THURSDAY: Scattered cloud cover, freezing level at valley bottom, light variable wind, no precipitation expected.

Avalanche Summary

On Monday our field team observed some size 2 natural avalanches on a north facing alpine feature east of Crescent Spur. These likely ran over the weekend.

On Sunday we received some great observations of avalanches running naturally on a crust in the trees in "The Farm" area, more details here.

On Friday our field team found stiff and heavily wind affected snow in the Renshaw. They spotted one size 2 wind slab that had released out of a NW facing chute, more details here.

Snowpack Summary

The region has picked up 20 to 50 cm of new snow in the last week with the weekend pulse coming in warm and wet. Another 5 to 10 cm is expected Tuesday.  

Underneath the storm snow you are likely to find a hard melt-freeze crust that can be found up to about 1600 m. You may also find buried surface hoar under the new snow which could make for touchy storm slabs. You are most likely to encounter it in terrain features sheltered from the wind, for example in openings below treeline. As the new snow continues to settle and forms slab properties, these layers could become reactive to human traffic. 

Around 60 to 130 cm of snow rests above a weak layer buried in early-December. On Jan 14th our field team found it in the Holmes area. This setup has created a persistent slab avalanche problem and a low probability/high consequence scenario. Depending on location, the buried weak layer is composed of surface hoar and/or a crust/facet combination. Reports suggest that this layer has become dormant in much of the region except for perhaps the Pine Pass area.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.
  • Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.