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Avalanche Forecast

Archived

Jan 21st, 2021–Jan 22nd, 2021

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

Regions

South Columbia.

Triggering avalanches may be possible in specific areas with stiff, wind-drifted snow or with a buried weak layer. Monitor for these conditions where you travel on Friday. 

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

Thursday night: Mostly clear, light northwest winds, alpine temperatures dropping to -20 C.

Friday: Mainly sunny, light northwest winds, alpine high temperatures near -14 C. 

Saturday: Partly cloudy, light variable winds, alpine high temperatures near -15 C.

Sunday: Increasing cloud, light south winds, alpine high temperatures near -12 C.

Avalanche Summary

Recent strong winds have formed wind slabs in lee features at upper elevations that may be possible to human trigger. With the strong winds on Tuesday, operators in the region reported small to large (size 1-2) wind slabs releasing naturally as well as several size 1-2 explosive-triggered cornices. 

On Monday and Tuesday, several operators in the region reported small (size 1-1.5) human-triggered avalanches releasing on a weak layer of surface hoar on north, east and southeast aspects at treeline and below treeline elevations. These avalanches were breaking 25-45 cm deep. 

Snowpack Summary

Recent winds have scoured snow surfaces, loaded cornices, and formed stiff wind slabs in alpine and upper treeline areas. These wind slabs sit over a variety of surfaces, including isolated surface hoar, sun crusts, and settling storm snow. A new sun crust may be forming on steep solar aspects, and there here have been reports of surface hoar growing on the snow surface.  

50-70 cm of snow from the past week has buried a weak of layer of surface hoar that is likely to be preserved in sheltered, open slopes at and below treeline. Observers in the south of the region continue to report sudden results in the snowpack tests and shooting cracks on this layer. Don't let benign weather lure you into complacency. Recent avalanche activity demonstrates that this layer is likely to be reactive where it is preserved and that it warrants careful assessment. Below 1700 m, 20-30 cm of snow is settling above a decomposing melt freeze crust. 

Deeper in the snowpack, a couple of older persistent weak layers may still be identifiable from late and early December, consisting of surface hoar and a crust with faceted snow and buried anywhere from 100-200 cm deep. Prolonged periods of inactivity and unreactive snowpack test results suggest that these layers have trended towards dormancy. 

Terrain and Travel

  • Carefully evaluate steep lines for wind slabs.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Avoid exposure to slopes that have cornices overhead.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.