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Avalanche Forecast

Archived

Mar 3rd, 2020–Mar 4th, 2020

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

Regions

South Columbia.

It's spicy out there right now. Between fresh wind slabs and a touchy persistent weak layer, human triggered avalanches are likely. Keep in mind it's not always the first rider who triggers the slab.

Confidence

Moderate - Forecast snowfall amounts are uncertain. Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.

Weather Forecast

Tuesday night: 5-20 cm new snow. Strong west wind. Freezing level 1200 m.

Wednesday: 5-10 cm new snow. Moderate northwest wind. Freezing level 1200 m.

Thursday: Flurries. Moderate southwest wind, strong at ridgetop. Freezing level 1700 m.

Friday: 5-20 cm new snow. Light southwest wind. Freezing level 1500 m.

Avalanche Summary

Since the weekend we have seen a surge in persistent slab avalanche activity on the February 22 surface hoar layer. Numerous skier triggered and remote triggered size 1-2 have been reported by nearly every ski operation region wide even as professionals tiptoe around, avoiding suspect terrain features. Observations are from all aspects and elevations, but especially concentrated on north to east aspects around treeline.

In several instances, slopes were ski cut with no results, only to have the third or fourth skier in the group accidentally trigger the slab. In other cases, avalanches were triggered on slopes with old ski tracks or where avalanches had already released.

Naturals triggered by cornice falls, loose snow running out of extreme terrain or warming temperatures were observed mostly around size 2, but up to size 3. Natural wind slab avalanches size 1-2.5 were observed on easterly aspects in the alpine on Sunday.

Snowpack Summary

New storm slabs are forming in snowier areas of the region, with 25 cm falling in some areas by end of the day Wednesday with light to moderate westerly wind.

A weak layer of widespread surface hoar sits 40-70 cm deep, ontop of a crust on solar aspects. The overlying snow has been cohered into slabs by incremental loading through successive storms, wind and mild temperatures. As slab character and depth increase, so do reactivity and size of avalanches failing on the weak layer. Read more about surface hoar on our forecaster blog!

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.
  • Surface hoar distribution is highly variable. Avoid generalizing your observations.
  • In times of uncertainty conservative terrain choices are our best defense.
  • Even brief periods of direct sun could produce natural avalanches.

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.