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Avalanche Forecast

Archived

Mar 17th, 2021–Mar 18th, 2021

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

Regions

Purcells.

Spring-like diurnal conditions exist and the rating reflects the highest hazard level anticipated during the day. Pay attention to steep south facing slopes as they heat up in the afternoon and possibly destabilize. Give looming cornices a wide berth from above and below. 

Confidence

Moderate - Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack.

Weather Forecast

A Pacific frontal system approaching the coast on Thursday will start to force some upper-level cloud cover to the Interior Mountain Ranges. Freezing levels will be between 1500-2000 m. By Friday the system will bring unsettled weather with new snow and cloudy skies.

Thursday: Mix of sun and cloud. Alpine temperatures near 0 and freezing levels 2000 m. Ridgetop wind strong from the South.

Friday: Mostly cloudy with 5 cm of new snow. Alpine temperatures near -1 and freezing levels 1800 m. Ridgetop wind moderate from the southwest.

Saturday: Mix of sun and cloud. Alpine temperatures near -6 and freezing levels 1500 m. Ridgetop wind moderate from the southwest.

Avalanche Summary

On Tuesday, natural cornice falls were seen. Reports indicated that they did not pull a slab on the slope below. Sunshine and daytime warming may initiate loose wet avalanches on steep solar slopes and continue to weaken cornices on Thursday.

Snowpack Summary

Surface hoar crystals can be found on Northerly aspects above 1800 m combined with dry wintery snow. On solar aspects and at lower elevations expect crusty snow in the morning and soft, moist snow in the afternoon. Large cornices may still pose a hazard close to alpine ridgelines, especially when it's warm and sunny.

A persistent weak layer of facets 40-60 cm deep that was buried in mid-February was reactive in the north of the region earlier this month but since the first week of March, only a couple of avalanches have been reported on this layer resulting from large triggers such as cornice fall. There are several other weak layers deeper in the snowpack composed of old surface hoar, facets and/or crusts, all of which have been recently unreactive.

Terrain and Travel

  • A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.
  • Back off slopes as the surface becomes moist or wet with rising temperatures.
  • Avoid exposure to slopes that have cornices overhead.
  • When a thick, melt-freeze surface crust is present, avalanche activity is unlikely.

Problems

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.