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Avalanche Forecast

Archived

Apr 5th, 2022–Apr 6th, 2022

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

Regions

South Coast Inland.

The recent storm snow is expected to remain reactive to human triggering, especially in wind-loaded terrain. With extended sun exposure on Wednesday, any unconsolidated storm snow may settle into a more cohesive slab and become increasingly reactive. 

Confidence

Moderate - Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack. Uncertainty is due to the limited number of field observations.

Weather Forecast

A ridge of high pressure brings sunny conditions for Wednesday morning but cloud from a storm system impacting the north coast may spill into the region by the afternoon. There is currently model uncertainty regarding how much cloud or sun the region will see Wednesday afternoon with one showing full sun and the other showing substantial cloud.

Tuesday Night: Mainly clear, moderate NW wind easing overnight, freezing level at valley bottom. 

Wednesday: Mainly sunny in the morning, a chance of increasing cloud cover in the afternoon, light SW wind, freezing level high around 1700 m.

Thursday: A mix of sun and cloud, light to moderate SW wind, freezing level high around 2500 m.

Thursday night and Friday: Precipitation 5-20 mm, a chance of sunny breaks in the afternoon, moderate to strong SW wind, freezing level falling to around 1400 m. 

Avalanche Summary

An early report from Tuesday includes observations of a few natural size 1 storm slabs in the Coquihalla area. 

On Monday, numerous natural storm slabs up to size 2.5 were reported in the north of the region, many of which likely occurred Sunday overnight during the peak of the storm. These were mainly on northwest through northeast aspects resulting from wind loading and were typically around 40 cm thick. Skiers and explosives also triggered a few small storm slabs in the north of the region. No new avalanches were reported in the south of the region but the number of observers is now very limited. 

Snowpack Summary

The recent storm typically produced 30-50 cm of new snow in the north of the region and 40-70 cm in the south of the region. This storm snow has buried a firm crust which extends to mountain top on solar aspects and to around 2200 m on northerly aspects. Strong to extreme southwest wind has redistributed the new storm snow in exposed, high elevation terrain forming wind slabs and developing large cornices. Windward slopes have been scoured down to the crust and the alpine snow surface is expected to be highly variable. 

The middle and lower snowpack are generally strong and well bonded. 

Terrain and Travel

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Minimize exposure to sun-exposed slopes when the solar radiation is strong.
  • 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.

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.