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Avalanche Forecast

Archived

Mar 28th, 2021–Mar 29th, 2021

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

Regions

South Coast Inland.

Be in initial assessment mode as you check out the outcome of the storm, especially if forecast snowfall is exceeded. Expect to find reactive new wind slabs in exposed terrain but keep your guard up in sheltered areas until you have good info about how the new snow is bonding.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Sunday night: Clearing. Strong northwest winds. Freezing levels returning to valley bottom.

Monday; Mainly sunny. Moderate to strong northwest winds. Alpine high temperatures around -9 with freezing levels to 1000 metres.

Tuesday: A mix of sun and cloud. Light variable winds shifting southwest. Alpine high temperatures around -3 with freezing levels climbing to 1600 metres.

Wednesday: Sunny. Light southwest winds. Alpine high temperatures around 0 as freezing levels climb to 2000 metres.

Avalanche Summary

A report from Mt. Rohr on Saturday showed a fresh cornice triggered slab from a steep piece of terrain, a great reminder of cornice and associated avalanche hazards.

Avalanche activity on Friday was limited to loose wet avalanches to size 1.5 from steep terrain facing the sun.

Looking forward, new snow from Sunday's storm may need a day to settle and form a good bond with the old surface. Extra caution should be taken in wind loaded areas, which may begin to include more south slopes as a forecast shift to north winds takes place.

 

Snowpack Summary

Up to 30 cm of new snow may accumulate by the end of Sunday's storm in the south of the region with likely closer to half that in the north of the region.

The new snow has buried a mix of widespread hard crust and a bit of moist new snow below about 1700 metres and to either sheltered low density or wind affected dry snow above this elevation. The lower snowpack is strong and settled.

Remember that cornices along ridgelines are large at this time of year and always have the possibility of failing naturally or from the weight of a human.

Terrain and Travel

  • Closely monitor how the new snow is bonding to the old surface.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent avalanches.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

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.