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Avalanche Forecast

Archived

Mar 26th, 2021–Mar 27th, 2021

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

Sea To Sky.

 Mainly overcast Saturday prior to the next round of precipitation on Saturday night into Sunday. 

Confidence

High - The snowpack structure is generally well understood.

Weather Forecast

FRIDAY Night: Cloudy with clear breaks, moderate northwest wind, treeline temperatures around -5 C, freezing level 1000 m.

SATURDAY: Mainly cloudy with sunny breaks and flurries in the afternoon, moderate southwest wind, treeline temperature around -4 C, freezing level 1100 m.

SUNDAY: Snow, accumulation 15-30 cm, moderate to strong southwest wind, treeline temperatures around -5 C, freezing level 1000 m.

MONDAY: Mix of sun and cloud, light north wind, treeline temperatures around -6 C, freezing level 800 m.

Avalanche Summary

A few cornices were triggered naturally and from explosives on Tuesday, Wednesday and Thursday. They were very large, as is expected at this time of year. On Thursday there was also a size 2 wind slab reported on a north aspect at 1900 m. 

Snowpack Summary

Snow accumulated earlier in the week with strong wind from the southwest switching to northeast. New wind slabs likely formed during this time, which may linger in steep, alpine terrain features. This snow adds to the 30+ cm that accumulated on the weekend. All of the new snow sits above a widespread crust, with the exception of high north-facing terrain. Observations suggest the snow has bonded well to the old snow beneath. 

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

  • Carefully evaluate steep lines for wind slabs.
  • 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

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.