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Avalanche Forecast

Archived

Mar 25th, 2021–Mar 26th, 2021

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

Regions

Northwest Coastal.

Recent snow continues to be wind-loaded into lee terrain features at upper elevations. Be on alert for signs of instability as you gain elevation. Cornices have been especially touchy recently so take extra precautions to avoid them.

Confidence

Moderate - Uncertainty is due to the extreme variability of wind effect on the snowpack.

Weather Forecast

Thursday night: Flurries bringing a trace. Moderate to strong northwest wind. Alpine temperatures around -6. Freezing level 500 m.

Friday: Flurries bringing up to 5 cm. Strong northwest wind shifting southwest. Alpine high temperatures around -4. Freezing level 1000 m.

Saturday: 10-20 cm new snow. Strong southwest wind. Alpine high temperatures around -4. Freezing level 1000 m.

Sunday: 10-20 cm overnight then clearing. Moderate westerly wind. Alpine high temperatures around -8. Freezing level 500 m.

Avalanche Summary

Explosive control work conducted east of Kitimat on Thursday revealed touchy cornices up to size 2.5, but stubborn wind slabs limited to size 1. Loose dry results were also observed up to size 1.5.

On Wednesday and Thursday, evidence of a widespread natural avalanche cycle was observed to have run during Tuesday's storm throughout the region. At upper elevations, avalanche character was storm slab mostly around size 2 and up to size 3 in coastal areas and Bear Pass. Below treeline, avalanche character was loose wet size 1-1.5.

Several natural glide slab avalanches have been reported over the last week size 2-3. Avoid slopes with glide cracks on them at all times. They are inherently unstable and can release at any time.

Snowpack Summary

Tuesday's storm dropped 30-50 cm of new snow over the region, falling as rain at lower elevations. This recent snow continues to be wind loaded into lee terrain features and cornices in the alpine and exposed treeline. Below treeline, surfaces fluctuate between moist and crusty depending on elevation and time of day.

A crust is buried 60-80 cm below the surface on solar aspects and below 1400 m. At higher elevations where this crust tapers out, the new snow has added significant load to a couple of deeply buried weak layers that we haven't quite ruled out as problems.

The first and most concerning is a roughly 70-100 cm-deep persistent weak layer of surface hoar buried March 12 on sheltered northerly aspects around treeline. Deeper down, around 100 to 300 cm now overlies another layer of surface hoar (and faceted snow) buried in mid-February that may still be a concern in shallower snowpack areas. Although they haven't produced recent avalanches, professionals in the region have been tracking and treating these layers with caution. If it hasn't already been occurring, there is a chance further loading during Tuesday's storm could result in some step-down activity to produce very large and destructive avalanches.

The mid and lower snowpack is well settled and strong in most areas.

Terrain and Travel

  • Be especially cautious as you transition into wind affected terrain.
  • Seek out sheltered terrain where new snow hasn't been wind-affected.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Extra caution is needed around cornices under the current conditions.

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.

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.