Avalanche Forecast

Issued: Apr 23rd, 2021 4:00PM

The alpine rating is moderate, the treeline rating is moderate, and the below treeline rating is low. Known problems include Storm Slabs, Loose Wet and Cornices.

Avalanche Canada swerner, Avalanche Canada

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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!

Summary

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

An icon showing Storm Slabs

New snow is forecast for upper elevations and the region may receive up to 40 cm by Sunday. Reactive storm slabs may exist if there is a poor bond to the old snow surfaces comprising of mostly crusts and firm snow on North facing alpine slopes.

Dry loose sluffing may be seen from steep terrain.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Loose Wet

An icon showing Loose Wet

Wet loose avalanches are possible below treeline with forecast rain. If a firm crust exists this problem is unlikely. 

Aspects: All aspects.

Elevations: Below Treeline.

Likelihood

Possible

Expected Size

1 - 1.5

Cornices

An icon showing Cornices

Cornices are at their largest at this time of year. They are weak and unpredictable. 

Aspects: North, North East, East, West, North West.

Elevations: Alpine.

Likelihood

Possible

Expected Size

2 - 3

Valid until: Apr 26th, 2021 4:00PM