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Avalanche Forecast

Archived

Apr 8th, 2022–Apr 9th, 2022

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

Regions

North Columbia.

Strong West winds and up to 20 cm overnight may build reactive wind slabs. 

The temperatures have dropped and so has the avalanche hazard. Keep in mind that persistent weak layers continue to linger, especially on high elevation slopes that remain winter-like.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

A cool and unstable weather pattern will exist through the weekend. Snowfall amounts vary widely across the region.

Friday Night: New snow 5-15 cm. Moderate to strong West winds at ridgetop and freezing levels near 1000 m. 

Saturday/ Sunday: Cloudy with possible sunny periods with new snow 5-10 cm. Light to moderate ridgetop wind from the northwest. Freezing levels 1000 m and dropping to valley bottom overnight. Alpine temperatures near -10 C.

Monday: Mix of sun and cloud. Freezing level near 1000 m and alpine temperatures -15 C. Ridgetop winds light from the West.

Avalanche Summary

On Thursday, two remotely (from afar) human-triggered storm slab avalanches were reported up to size 2 as well as numerous natural wind slabs and cornice failures up to size 3. During the warming, numerous wet loose avalanches were also seen up to size 1.5 mostly from steep slopes and terrain features. 

Earlier this week, reports showed a wide range of avalanche activity. A natural storm/ wind slab and wet loose cycle were seen up to size 2.5. A few human-triggered avalanches up to size 2 and some larger size 3 persistent slabs that possibly failed on the late March crust. Upon further investigation, a persistent slab that was triggered by explosive control (reported Tuesday) was said to have failed on the end of March crust and stepped down to the early December rain crust that sits approx. one metre off the ground. That avalanche was a size 3.5. 

Snowpack Summary

A surface crust may exist on solar aspects up to the mountain top and on north-facing aspects up to 2000 m. 

Over the past week, up to 50 cm of storm snow blanketed upper elevations. Light to moderate wind may have redistributed the storm snow in exposed high elevation terrain forming wind slab and large cornices. 

The new snow brings up to 80 cm above the crust from late March. This crust is present on all aspects up to an elevation of 2500 m. Large avalanches have failed on this crust over the past few days. 

The early-December rain crust is approximately a metre off the ground. Large slab avalanches failed on this interface last week following a rain and warming event. 

These persistent weak layers are expected to become dormant after being tested by warming followed by cooling temperatures. 

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Be aware of the potential for large avalanches due to the presence of a buried crust.
  • Wind slabs may be poorly bonded to the underlying crust.
  • 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.