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Avalanche Forecast

Archived

Mar 25th, 2022–Mar 26th, 2022

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

Regions

Northwest Coastal.

Carefully assess steep lines for wind slabs and limit exposure to cornices. We have some uncertainty in the likelihood of triggering persistent slab avalanches.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

Friday night: Possibility of light flurries bringing trace amounts of new snow with light east winds. Low of -2 at 900 m.

Saturday: Flurries bringing around 5 cm. Light to moderate southeast wind. Freezing level 1100 m.

Sunday: A mix of sun and cloud with the possibility of light flurries bringing trace amounts of new snow. Light variable winds. Freezing levels rising to 1400 m.

Monday: Sunny with no new snow expected and light west winds. Freezing level rising to 1500 m.

Avalanche Summary

On Thursday a size three natural persistent slab avalanche was reported . This avalanche ran on the mid March surface hoar layer. It was at 1600 m on a northeast aspect. Several natural and explosive triggered cornice falls up to size three were also reported throughout the region. Natural and explosive triggered wind slabs were observed to size 1.5.

Touchy avalanche conditions on Wednesday saw skiers and machines remotely triggering storm slabs size 1.5-2. We're scratching our heads over a report from near Ningunsaw of a skier-triggered size 2.5 and sympathetic size 2 deep persistent slab. The avalanches occurred on a west aspect around 1200 m and crown depths varied from 40 cm to 120 cm.

Snowpack Summary

30-50 cm of recent snow has seen variable wind effect at upper elevations. Below 1500 m, recent snow tapers in depth and sits over a wet or crusty upper snowpack.

A weak layer of surface hoar from mid March buried 70-120 cm deep has become more difficult to trigger but recent avalanche observations indicate that it may continue to be problematic. 

A thick rain crust from mid-February 130-200 cm deep caps a well consolidated lower snowpack.

Terrain and Travel

  • Be especially cautious as you transition into wind affected terrain.
  • Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • When a thick, melt-freeze surface crust is present, avalanche activity is unlikely.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

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.