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Avalanche Forecast

Archived

Mar 28th, 2021–Mar 29th, 2021

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

Regions

South Columbia.

Overnight snow and moderate wind shifting northwest will continue to build touchy slabs and elevate avalanche hazard at upper elevations. Crusty surfaces below treeline will make for low hazard but difficult travel conditions.

Confidence

Moderate - Forecast snowfall amounts are uncertain. Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

Convective instability behind the storm will bring additional snowfall to some areas overnight Sunday and into Monday. Specific locations and amounts are notoriously difficult to forecast for this type of weather pattern.

Sunday night: 5-15 cm new snow. Moderate to strong northwest wind. Freezing level drops to valley bottom. Alpine temperature -11.

Monday: Flurries bringing a trace of new snow. Moderate northwest wind. Freezing level 800 m. Alpine temperature -12.

Tuesday: Mostly cloudy. Light westerly wind. Freezing level 1500 m. Alpine temperature -5.

Wednesday: Sunny. Light southwest wind. Freezing level 2100 m. Alpine temperature -1.

Avalanche Summary

We are still awaiting reports of avalanche activity from the weekend's storm. A widespread natural cycle is likely to have occurred Sunday.

There have been a few notable slab avalanches over the past week. On Saturday, several natural cornice falls triggered size 2-3 avalanches. One of which is suspected to have run on a deeply buried crust near the base of the snowpack. On Thursday a natural size 3 was observed on a east aspect at 1800 m in the Valhallas. The crown was 100 cm thick, but no other details are known. On Wednesday there was a size 2 skier triggered avalanche on a east facing slope at 2250 m in the southern Selkirks, running on a 30 cm deep crust layer.

Snowpack Summary

The weekend's storm dropped 20-40 cm over the Selkirk mountains and 5-10 cm in the Monashees. This snow has likely been redistributed by strong wind, switching from southwest to northwest Sunday night. Crusty surfaces exist below treeline.

At alpine and treeline elevations, a few layers of note are buried 40-80 cm deep including a layer of small surface hoar crystals on shady, wind-sheltered aspects and a series of crusts on solar aspects and below 1800 m. Overall the snow seems to be bonding well to these interfaces, although there have been a few isolated avalanches running on crusts layer over the past few days.

Terrain and Travel

  • Be careful to keep storm day fever from luring you out into bigger terrain features.
  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Seek out sheltered terrain where new snow hasn't been wind-affected.
  • Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.

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.