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Avalanche Forecast

Archived

Mar 4th, 2021–Mar 5th, 2021

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 possible, human triggered probable.
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.

Warm temperatures and sunshine will elevate avalanche conditions, especially on south-facing slopes.

Confidence

Moderate - Uncertainty is due to how the snowpack will react to the forecast weather.

Weather Forecast

Another day of warm sunny weather then some clouds and light flurries over the weekend.

THURSDAY NIGHT: Partly cloudy, moderate southwest wind, a weak temperature inversion may develop overnight with alpine temperatures in the -2 to 0 C range and cooler in the valleys.

FRIDAY: Mostly sunny with some afternoon clouds, moderate south wind, freezing level around 2000 m with treeline temperatures near 0 C.

SATURDAY: Cloudy with scattered flurries and 5-10 cm of new snow, light southwest wind, freezing level climbs to 1400 m with treeline temperatures near -3 C.

SUNDAY: Cloudy with another 5-10 cm of new snow, light south wind, freezing level around 1300 m with treeline temperatures near -5 C.

Avalanche Summary

Preliminary reports from Thursday suggest warm weather resulted in widespread wet loose avalanches on steep south-facing terrain as well as a few natural wind slab avalanches on south aspects. On Wednesday, in addition to wet loose avalanches, there were a few human triggered slab avalanches showing the impacts of warming on slab avalanche conditions. Two notable incidents were on south-facing slopes in Glacier National Park, including a size 3 wind slab avalanche in a steep alpine couloir (MIN report) and a size 1.5 slab avalanche in below treeline terrain (MIN report). 

Warming is expected to cause heightened avalanche conditions again on Friday. Read more in this Forecaster Blog.

Snowpack Summary

Rising freezing levels and sunshine will be melting, and potentially destabilizing, snow surfaces the next few days. Higher elevations have been impacted by recent wind from the southwest, likely leaving wind slabs lurking on shaded north and east slopes.

The lower snowpack has been strengthening with reactivity on persistent weak layers on the decline. The two layers of concern have been a layer of facets that was buried in mid-February (60-100 cm deep) and a layer of surface hoar and/or crusts that was buried in late January (80-120 cm deep). The current impulse of warming will likely be the final test on these layers, as there is some uncertainty about whether they will become reactive again under these conditions.

Terrain and Travel

  • Avoid exposure to steep, sun exposed slopes, especially when the solar radiation is strong.
  • If you are increasing your exposure to avalanche terrain, do it gradually as you gather information.
  • The more the snowpack warms-up and weakens, the more conservative you`ll want to be with your terrain selection.
  • Be careful as you transition into wind affected terrain.
  • Cornices become weak with daytime heating.

Problems

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

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.