Avalanche Forecast

Archived

Apr 9th, 2021–Apr 10th, 2021

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 unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

Sea To Sky.

Ease into terrain cautiously with an assessment mindset on Saturday and expect the reactivity of new snow to increase with elevation and wind effect. Be especially cautious around steep slopes being hit by the sun. This is where natural avalanches will be most likely.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Friday night: Continuing snowfall bringing new snow totals to 15-25 cm. Strong southwest winds shifting west as snowfall eases.

Saturday: A mix of sun and cloud. Light to moderate northwest wind. Alpine high temperatures around -9 with freezing levels to 1000 metres.

Sunday: Mainly sunny. Light variable winds. Alpine high temperatures around -5 with freezing levels to 1500 metres.

Monday: Sunny. Light northeast winds. Alpine high temperatures around -3 with freezing levels to 1700 metres.

Avalanche Summary

Fresh storm slabs will continue build overnight and will very likely be reactive to human triggering on Saturday, especially where wind loading occurs. Expect snow to shed naturally from sun-exposed slopes during the day.

Small (size 1) natural wind slab were observed with ongoing wind transport of recent snow in the Whistler area on Thursday.

A natural avalanche cycle was observed in the region on Saturday during the last storm. On Sunday, there were a few size 1-1.5 human triggered wind slab avalanches reported. This MIN describes triggering a small wind slab in large terrain.

Snowpack Summary

15-25 cm of new snow is expected to accumulate by Saturday morning, bringing the total this week to about 25-40 cm. Strong southwest winds are expected to accompany the new snow, likely forming fresh and reactive slabs in many areas.

The recent storm snow sits on a crust on sun-exposed aspects, and on all aspects below about 1600 m. It likely sits on soft snow or wind slabs on north aspects.

Cornices are large and looming along ridgelines. Their release is unpredictable, requiring a large berth if you're travelling above or below them.

Terrain and Travel

Continue to make conservative terrain choices while the storm snow settles and stabilizes.
Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
Choose conservative terrain and watch for clues of instability.
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.