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Avalanche Forecast

Archived

Apr 3rd, 2021–Apr 4th, 2021

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

Purcells.

Winter is still hanging on in the alpine, with a fresh hit of snow arriving overnight. The new snow may be reactive in wind loaded features or where it sits over a crust. Check out our latest forecaster blog on managing these not-quite-yet-spring conditions. 

Confidence

Moderate - Forecast precipitation (either snow or rain) amounts are uncertain.

Weather Forecast

Light precipitation spreading north to south overnight Saturday into Sunday. Local enhancements of up to 20 cm may be found on southwest facing slopes along the western border of the region. Below the freezing level, precipitation will fall as light rain.

Saturday night: 5-10 cm in the north of the region. Moderate to strong southwest wind. Alpine temperatures around -3. Freezing level 2000 m.

Sunday: 5-10 cm in the south of the region. Light southwest wind shifting northwest over the day. Alpine high temperatures around -5. Freezing level 1800 m.

Monday: Sunny. Light to moderate northwest wind. Alpine high temperatures around -1. Freezing level 2100 m.

Tuesday: Sunny. Light to moderate south wind. Alpine high temperatures around -1. Freezing level 2300 m.

Avalanche Summary

Cornices have been reactive to explosives, but have not been observed to trigger slabs on slopes below. A natural size 3 was reported on Thursday in the Dogtooth range. It was on a southeast aspect in the alpine and is suspected to have solar-triggered and run on the crust buried in mid-March.

Reports from Wednesday included small (size 1) wet loose point releases from steep solar aspects and explosive triggered wind slabs on north to east facing ridgetops.

Snowpack Summary

Surface melt-freeze crusts exist on solar aspects and below about 2000 metres. Above this elevation, 15-40 cm of recent snow has otherwise seen some redistribution by southwest to northwest wind, and seems to be bonding well with underlying surfaces.

A widespread crust layer from the mid-March warm spell can be found 30-60 cm deep, and small surface hoar has been observed at this depth on some isolated north-facing slopes. Reports suggest the snow is generally well bonded to these layers but isolated instances of large solar-triggered slab avalanches running on the crust have been observed. Deeper layers are strong and have been unreactive over the past few weeks.

Terrain and Travel

  • Closely monitor how the new snow is bonding to the crust.
  • Watch for wind-loaded pockets especially around ridgecrest and in extreme terrain.
  • Extra caution is needed around cornices under the current conditions.
  • A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.