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Avalanche Forecast

Archived

Feb 28th, 2021–Mar 1st, 2021

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.
Below Treeline
Natural avalanches unlikely.

Regions

Sea To Sky.

A bit of new snow with strong wind will keep wind slabs fresh Monday. Keep an eye out for wind affected snow on atypical aspects and lower-than-usual elevations due to recent variable wind direction and elevation.

Confidence

Moderate - Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack.

Weather Forecast

Sunday night: Light flurries bringing a trace of snow. Freezing level 1100 m. Strong southwest wind affecting all elevations.

Monday: 5-10 cm new snow. Freezing level 1400 m. Strong southwesterly wind affecting all elevations.

Tuesday: Around 5 cm overnight then clearing. Freezing level 700 m. Light to moderate southwesterly wind.

Wednesday: Mix of sun and cloud. Freezing level 1300 m. Light to moderate southwesterly wind.

Avalanche Summary

By Saturday, reports of natural and human triggered avalanche activity quieted down but cornices continued to be reactive to explosives size 2-2.5. Minor pinwheeling was observed on steep solar aspects in the afternoon. On Friday, storm/wind slabs were reactive to human triggers around treeline to size 1. A natural avalanche cycle up to size 3 occurred during the storm on Thursday, primarily on north to east aspects 1500 to 2000 m.

Snowpack Summary

20 cm of recent snow overlies a variety of old surfaces including facets, spotty surface hoar in wind sheltered areas around treeline, a sun crust on steep solar aspects and a rain crust below 1500 m. Upper level wind, having recently shifted northwest is likely transporting the recent snow into wind slabs in a reverse-loading pattern in exposed features at upper elevations. Older wind slabs formed by previous southwest winds may also remain reactive to human triggers.

Another 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

  • Keep your guard up at lower elevations. Wind slab formation has been extensive.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Minimize your exposure time below cornices.

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.