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Avalanche Forecast

Archived

Mar 24th, 2021–Mar 25th, 2021

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 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, human triggered possible.

Regions

Cariboos.

Don't let the new snow lure you into consequential avalanche terrain, storm slab avalanches may be primed for human triggering.

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

WEDNESDAY NIGHT: Cloudy with some lingering flurries delivering up to 5 cm, 30 km/h northwest wind, treeline temperatures drop to -8 C.

THURSDAY: Mostly cloudy with some light flurries but no notable accumulations of snow, 30-40 km/h northwest wind, treeline temperatures around -7 C.

FRIDAY: Cloudy with some light flurries but no notable accumulations of snow, 20-30 km/h west wind, treeline temperatures around -5 C.

SATURDAY: Cloudy with scattered flurries and 5-10 cm of snow, 30-50 km/h southwest wind, freezing level climbing to 1900 m, treeline temperatures around -3 C.

Avalanche Summary

The North Rockies field team reported rapidly growing storm slabs producing shooting cracks in the northern part of the region on Wednesday (check for an upcoming MIN report from Sugarbowl). While we do not have other recent observations, the sheer amount of new snow on Wednesday likely resulted in natural avalanche activity at higher elevations and has left the potential for large human triggered storm slab avalanches at all elevations on Thursday.

Snowpack Summary

By the time Wednesday's storm ends we can expect 30-60 cm of fresh snow across the region. The heaviest accumulations appear to be northern parts of the region along the Robson Valley. We expect a fair bit of variability in the density of this new snow including heavier powder at lower elevations, deep low density snow at higher sheltered terrain, and firmer wind slabs in open terrain. Slightly beneath this new snow is a widespread crust layer from the mid-March warmup. While we don't have recent observations of this layer, we suspect the snow is bonding to this interface.

It appears persistent weak layers have gone inactive in the past week. We had been concerned about a weak facet layer from the mid-February cold snap that is now 80-120 cm deep. This layer resulted in a few large avalanches triggered by cornice falls in the first half of March, but recent weather patterns have helped this layer heal.

Terrain and Travel

  • Stick to well supported, lower angle terrain.
  • Keep your guard up at lower elevations. Storms slabs have been reactive at all elevations.
  • Avoid freshly wind loaded terrain features.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.