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Avalanche Forecast

Archived

Mar 18th, 2020–Mar 19th, 2020

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

Regions

South Columbia.

Wind slabs may still be found and deeper layers may still persist. Make observations and assess conditions continually as you travel.

Confidence

Moderate - Uncertainty is due to limitations in the field data.

Weather Forecast

Wednesday night: Mostly clear, light north wind, alpine temperature -11 C, freezing level at valley bottom.

Thursday: Mix of sun and cloud, light southeast wind, alpine temperature -4 C, freezing level 1500 m.

Friday: Mostly clear, light west wind, alpine temperature -4 C, freezing level 1700 m.

Saturday: Mix of sun and cloud, light west wind, alpine temperature -3 C, freezing level 1700 m. 

Avalanche Summary

Over the past several days, avalanche activity was reported as natural loose wet avalanches (size 1-2) running in steep, sun-exposed terrain in the alpine. Cornices were also observed failing naturally, primarily on north, northeast, and east aspects.

Reports from the weekend show several natural wind slab avalanches ranging in size from 1.5 to 2.5 running in the alpine on east, southeast and north aspects at treeline and in the alpine. There were also two reports of natural size 2 and 3 persistent slab avalanches running on the late February surface hoar layer. These were on west and southwest aspects between 1700 m and 2200 m and were 50-100 cm deep. 

The number of data sources for the region is diminishing as professional operations close. If you're spending time in the mountains, consider sharing your observations via the Mountain Information Network. Heightened diligence and conservative risk management is recommended at this time.

Snowpack Summary

Previous moderate to strong northeast and east wind redistributed snow and formed wind slabs that may remain possible to trigger in isolated areas. With recent sun and relatively warm temperatures, expect to find either moist surface snow or crust on slopes facing the sun. New snow from last week may sit on a weak surface hoar layer and a sun crust on steep solar aspects.

A widespread weak layer of surface hoar is buried 60-120 cm deep. Sheltered north, northeast, and east facing slopes near treeline are the most likely locations to find this layer and where avalanches have shown reactivity within the past week. Though there is a low likelihood of triggering an avalanche on this layer, the consequences of doing so would be high. Read more about surface hoar on our forecaster blog.

Terrain and Travel

  • Small avalanches can have serious consequences in extreme terrain. Carefully evaluate your line for wind slab hazard before you commit to it.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.
  • Make observations and assess conditions continually as you travel.

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.