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Avalanche Forecast

Archived

Mar 3rd, 2021–Mar 4th, 2021

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

Regions

Sea To Sky.

Check steep or confined lines for wind slab or wet surface snow before committing and give cornices a wide berth from above and below. 

Confidence

Moderate - Uncertainty is due to difficult to forecast freezing levels.

Weather Forecast

Wednesday night: Mostly cloudy, strong south wind above 2000 m, freezing level dropping to 1000 m. 

Thursday: Increasing cloud, scattered flurries with up to 5 cm of snow beginning in the afternoon, strong south wind, freezing level rising to 1600 m.

Friday: Overcast, 30-40 cm of new snow, strong south wind with extreme gusts, freezing level near 1300 m. 

Saturday: Mostly cloudy, 5-10 cm of snow, light southwest wind, freezing level near 1000 m. 

Avalanche Summary

Large cornices (size 2) continue to be reactive to explosives. Explosive mitigation since Monday has also triggered a small (size 1) loose dry and storm slab avalanche. Minor pinwheeling has been observed on steep solar aspects in the afternoon.

Snowpack Summary

A slight rise in temperature and 5-10 mm of precipitation beginning in the afternoon on Thursday may increase the potential for wet loose avalanche activity on slopes experiencing warming for the first time. Watch for pinwheels and roller balls, as they are a clear indication of this problem. You can avoid them by staying off steep slopes when the snow becomes wet or slushy. 

Strong winds from the south at upper elevations have formed shallow wind slabs in lee terrain features that may be possible to trigger. Recent winds have varied in direction, so watch for wind slabs on a variety of aspects. 

In sheltered areas, 20 cm of recent snow sits over a layer that may consist of of facets, spotty surface hoar, and/or crusts on steep solar aspects and below 1500 m. A weak layer buried in mid-February is composed of a crust, facets or spotty surface hoar depending on elevation/aspect, and is now down 50-80 cm. There have been no recent avalanches reported on this layer. Large triggers, such as an avalanche in motion, cornice fall, or intense loading from snow, wind and/or a rapid rise in temperature could awaken these deeper weak layers.

The mid and lower snowpack is well settled and strong in most areas.

Terrain and Travel

  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Carefully evaluate steep lines for wind slabs.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • Extra caution for areas experiencing rapidly warming temperatures for the first time.

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

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.