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Avalanche Forecast

Archived

Apr 23rd, 2021–Apr 26th, 2021

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

Regions

Sea To Sky.

Up to 40 cm of new snow is forecast for upper elevations by Sunday. This may build new and reactive storm slabs at treeline and in the alpine. 

This is the last forecast of the season.

Thanks for the great winter and play safe!

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

A weather system will approach the BC coast today. Tonight, the system will pivot towards the southern half of BC. The system will stall over southern BC tonight through the weekend resulting in persistent rain showers and alpine snow. The convective nature associated with this system could bring higher localized precipitation amounts.

Friday Night: Snow 3-10 cm. Winds light from the southeast. Alpine temperatures near -1 C and freezing levels 1500 m.

Saturday: Snow 5-10 cm at upper elevations. Wind light from the South. Alpine temperatures near -! and freezing levels 1600 m. 

Sunday: Snow 10-15 cm at upper elevations. Light wind from the South. Alpine temperatures -2 and freezing levels 1500 m. 

Monday: Snow 5 cm. Light-moderate wind from the southwest. Alpine temperatures near -4 and freezing levels 1500 m. 

Avalanche Summary

At treeline and in the alpine, the new snow combined with light to moderate wind may build fresh and reactive storm slabs. The new snow may have a poor bond to the old snow surfaces which are mostly crusts. Below treeline will see rain that will keep snow surfaces wet and weak. Loose wet avalanches are possible. 

Cornices remain weak and fragile. They require a large berth from above and below as they are very unpredictable.

Over the past week, the region saw intense warming and sunshine. This resulted in a widespread natural avalanche cycle up to size 4. Many of these involved the full depth of the snowpack, running to the valley bottom. Last weekend, multiple large to very large wet slab avalanches were observed near Whistler, size 2-4. Many of these involved the full depth of the snowpack, running to the valley bottom.

 

Snowpack Summary

New snow will accumulate at treeline and in the alpine through the weekend building fresh and reactive storm slabs. Below treeline elevations will likely see rain. The new snow will be landing on a melt-freeze crust that extends to the alpine on solar slopes and 2100 m on polar slopes. It may bond poorly. Rain below treeline will likely keep the snow surfaces wet and weak.

Cornices are large and looming along ridgelines. They are weak and very unpredictable. 

Terrain and Travel

  • Watch for fresh storm slabs building throughout the day.
  • Storm slab size and sensitivity to triggering will likely increase through the day.
  • Be alert to conditions that change with elevation and wind exposure.
  • A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.
  • 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.

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.

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.